54R Bren Issues

Greetings all: I have a MKII rebuilt by Len Savage. It's in 54R. Had a big issue with it today. Took it to the range and had several blown cartridges and then.... it fired out of battery and blew up (more specifically, blew the mag right out of the magwell and about 15 feet from where I was shooting. Seems to me that the barrel is cut to allow a part of the round to be unsupported and it further seems that it is exactly in that spot that the rounds are blowing out. This was happening before and I sent it back to the builder. He replaced the barrel and it is still having this issue. Ideas?[IMG][/IMG]
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He's chambered an existing barrel and now the extractor recess is too low. The cartridge shows two shoulders as if the 303 is still there and then the 7.62x54 was done.

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Originally Posted by browningautorifle

He's chambered an existing barrel and now the extractor recess is too low. The cartridge shows two shoulders as if the 303 is still there and then the 7.62x54 was done.

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Can anything be done? Or can a new barrel be cut w/o making the shoulders too low? Unlikely you're going to find an unissued Bren Barrel, so I assume they all start cut for .303 and then have to be reamed for 54r.

As in adding on to the back? I can't do it...maybe one of these guys has a solution. Give it a minute. Peter will be along...he's done a few things with these.

Thanks Jim. Builder just doesn't see it. Seems obvious to me that the cases are not supported there and that they blow out. Although only 5-6 of the 200 I have fired so far have, I think he's relying too much on the case wall.

He is. It's the sort of thing you see when amateurs ramp their .45 barrels or other pistols for easy feeding of non round nose bullets. They end up with a blow out exactly like yours. His is a bit shocking to me when I see he just ran in the ream. OOPS!

That's pretty ugly right there.

The double shoulder is just nasty.

For the STEEL -cased ammo to have blown out at the web indicates that there was WAY more pressure after ignition than is healthy for gun or driver.

Find a REAL gunsmith and get the "LEADE" of the barrel, just forward of that "interesting" chamber gauged up.

IF the 7.62 x 54R reamer did NOT cut its full "leade" then, on ignition, the projectiles may well have been "held" a little firmly, with the associated "spike" in pressure.

Also, beware of "interesting" 7.62 x 54R ammo: some of the stuff out there may well be "safe" in the Russian or Chinese machine-guns for which it was loaded, but would produce results like yours in a barrel that does not provide full support.

Also, check how hard the extractor (if you still have it) is "gripping" the case and whether it has been "adjusted for the fatter Russian cartridge.


At least you can play with such fun toys..........

My only experience with an absolute and total bodge like this is a Vickers modied to take 7.62 x54R steel cased ammo. Extractors widened to take the slightly wider base rim diameter. Chamber reamed to take 7.62mmx54R. But the old forward section of .303" chamber remains and shows on the fired rounds. BUT, it seems to 'work'....... in much the same way as an old land-rover 'works'

I'm not sure that the extractor way is not too low but put my money in BinO's house in that the ppressure inside the case is far to high and as such WILL take the line of least resistance and pop the unsupported side of the round. It will not do this with a .303" round.

I would try 7.62mm x54 brass cased ammo and ..........., well, see what happens. On the other hand, I would only do the job properly in the first place.

Looking at a couple of extractors and spent cases I suspect that the standard .303 extractor wouldn't be a problem dealing with/supporting the 7.62x56. The breech block will have had to be machined to accept the slightly larger rim dia though

Guys,

I converted a MKII to shoot 54r. I have had no problems. I reamed the barrel myself and modified the Breech block as Peter noted. Before reaming I drove in a plug so that when I reamed I had a correct chamber, no double shoulders. Over on the WeaponsGuild Board many of the guys have used the 54r conversion with the double shoulders with no problems and there have been no reports of blowouts such as djandj has experienced. There have been case separation problems which have always been traced back to excessive headspace.

I would definitely check the headspace before I went any further. If the case gets too far back it probably will blow.

The blown-out case appears to have a very short or no "solid" section at the rear of the case. I'd be very suspicious of the ammo being used. After one blow out, another should never have been fired until the problem was solved.

Below are two pics of a cartridge in a .303 bren barrel . One is a .303 British (left) and one is a 7.62x54R (typical Bulgarian light ball silver tip) in a rechambered Bren barrel. The .303 is fully supported in the extractor cut-out. The 54R maybe slightly less but it is steel.

I'd be looking at headspace issues or ammunition. I doubt the reaming, double shoulder or not has anything to do with the problem, My 2 cents.

Joe

Thanks Peter. The entire point of the build is so I DON'T have to use a dollar a round ammo! Going back to brass 54r is not the way I want to go. This SHOULD be able to use the cheap Russian stuff. To make things more confusing, I did fire over 100 rounds with NO problems and NO case issues (I checked the spent casings) So..... ammo variance could be part of this, but.... Without proper support, no casing can support the explosion.

With the varying posts, I'm confused and don't know which way to go. Can the low spot be welded up and fixed?

Just a couple of things - this has sort of whetted my appetite a bit in a strange way. I appreciate Joe's straight talkin' approach and the photos certainly show that there's plenty of meat in the case where the extractor slot is. I accept that if .303" brass ain't blowing out (and never has) then 762x54 steel should eaasily pass! But why. There's a simple answer coming up......

Djan.... I take the point and I agree about the cheapest ammo but when you go down that route, there is a chance that you will encounter a problem. And here it's a mechanical one. I don't agree that there ISN'T proper support because we've already shown/proved with 90% of the rounds and a lifetime of .303 rounds fired that even though there is an extractor slot, there definately IS proper support and the shell casings CAN support the load.

BUT......., some of them cannot support this. I would be finding the ammo type/make that WAS capable of supporting the load without splitting/rupturing and then concentrate on that ammo.

When you say 'the low spot' DJ, what do you mean? There are two 'low' spots on the rear face of a Bren barrel. The top 'low spot (1st and 4th photo) is to allow the slightly overhanging breech block feed horns a running clearance but clearly this isn't anything to do with your prob. Then there's a low part at the bottom of the barrel (2nd photo) the area of which is the cut-out that's causing the weak case to blow out. You can't do anything about this because it's the extractor way and the extractor on a Bren gun is a wonder of mechanical complexity because due to...... Do you want a slightly technical classroom lesson........ ? Anyway when the case is fully chambered and about to fire, the piston extension loosens its 'grip' on the extractor stay and loosens up the extractor on the about to be fired case.

Then after it's fired, the piston extension moves slightly rearwards and causes the extractor stay to REALLY tighten up on the case......... Now something else happens if you're following me....... The tight extractor is still gripping the red hot fired case as the breech block starts to drop down at the rear at commencement of unlocking and as it does, the lowest points at the face of the breect block violently rocks/rotates on the breech block stops in the gun body ( a major test by Armourers for worn guns) and the front rounded surface of the still tight extractor rocks on the extractor way in the barrel. The fired case is just gently rolled a gnats knacker to the rear and this gentle rolling motion just breaks the tight taper obturating seal of the case in the chamber. Now as the breech block has reached the unlocked point, it can move violently rearwards taking the loose case with it. In fact, it's SOOOOO violent, if the firing pin didn't punch a huge oval dish into the primer to swell it up and the ejector didn't additionally stake it in place to make sure, momentum would be freeing the primers out into the guns and causing jambs

That's why we rarely ever get ruptured cartridges in Bren guns. We DO of course but while the main extraction and ejection is violent, the actual PRIMARY extraction is a very quick, rolling leverage motion. That's why you can't weld up the hole or change the size to suit.

Sorry it's been a bit long winded...................

Good pics Joe. Very clear illustration ... I suspect steel case ammo doesn't offer the same support at the head. Maybe it's just inconsistent.

I don't know if anyone else would use weld at the edge of the chamber, it changes the metal somewhat. I have done that sort of thing before though and other things that could be de-cried as heresy if I told them. You'll have to decide how far you want to go to fix this.

I hope I've explained why that would be difficult BAR. I agree with Joe's great pictures. If I was still at work I'd ask the Armourters shop to have a look-see. I'm inclinbed to agree that DJ shoulkd be free to use the cheap stuff but select the cheap stuff that works

Guys,

If you look at the blow out on dandj's case it doesn't appear that it has the same solid head depth as the 54r case in my picture. In addition to my eyeball, I did a little "scaling" of my case and his pic to come to that conclusion. If that is true then the ammo is the problem. It may not be the typical light ball.

If the headspace is "loose" and the ammo is short on the height of the solid section then you can easily get the blow out.

I'd check out the ammo first. Take an unfired case, remove the bullet and powder, fire the primer, and half section it with a dremel cut off wheel just as I did and check it in the barrel for support. If that checks out then check the headspace. One other possibility with a semi -auto is to check to be sure the bolt carrier is in the correct position relative to the breech block when it is in battery. The mechanism is designed so that the piston and carrier move about a 1/2" rearward before the bolt unlocks, so that the bullet has exited the barrel and the pressure has dropped. If the carrier is not far enough forward the bolt may unlock prematurely causing the blow out.

I don't know how your Bren is configured. I've located the tab on my striker such that it can't hit the firing pin unless the carrier is fully forward preventing out of battery discharge and the problem discussed above. Not an issue with the original FA Brens.

I searched on another board regarding Bren headspace issues. A poster was having problems with a semi bren. The .303 cases were separating about 3/4 the way up the case. He also mentioned he was "blowing out " 54r cases at the base (no pics). He posted a pic of the rear of the breech block / locking shoulder when in battery. You could throw a cat through the crack, well maybe .030". He had ground the locking shoulder too far back after welding. He replaced the locking shoulder and set the headspace properly and the problems disappeared.
Joe

I.m not familiar with the semi auto guns but when yoiu mention CHS with the standard guns (.064go and .074" no go AS A RULE OF THUMB HERE.....) it's worth remember int that conjoined with those measurements was also the running clearance and end float ON TOP of the CHS. To put things into perspective, to assemble up a Bren from parts after repair on a bench, ready for dry testing or function testing on the bench, then range function testing was given as 1.6 hours. 1 hr 36 minutes. Add to that anything else like pairing up/mix and matching barrels, changing locking shoulders etc etc.

No wonder when I asked my old pal Roger about this he just sighed and said '....... I xxxxxxg hated them. Not enough hours in the day..........'

Thanks for all the help guys. Let me know if you want more pics and of what. It seems clear to me that this is a problem with the gun as well as the ammo. While as I said, I have fired about 150 rounds with this barrel and gun set up, having up to 5 blowouts is dangerous and unacceptable. As for the ammo? Well, it was standard Russian Silver tipped 147g light ball. While I did not same the spam can top, the bottom is marked D(in cyrilic) 64. Other than that, it looks identical to all the other stuff. As I said, this particular set up has always had a problem with blowouts. The first time the builder sent it to me, it would "harmlessly" blow out the same spot along the rim, but would not interrupt operations. Since he rebarreled it, it now does what you see. When these blowout occur, the gun freezes up as the round is locked in the chamber and I have to use a hammer to bang the charging handle back to get the spent casing out of the barrel. True it did not do it with the previous spam can I had and so far has done it 5 times our of 80 round fired in that particular spam can. While I can certainly change spam cans, the point is what good is a $4K 23 pound rifle that is prone to blowing up if I hit the wrong round in otherwise indistinguishable spam cans? Some have commented above that the work was done wrong. Others say no. I certainly have no idea. I can change spam cans and hope I don't get blown up. But it wasn't alot of fun watching the steel magazine flying out of the gun and landing 10 feet from me.

Peter, thank you so much for the fantastic information. However, I still don't have an answer. The builder looked at my pics and said the headspacing looked right. IDK. My next thought is to send it to Troy and Barrelxchange as he does 54R conversions and let him look at it. He looked at the pics and also though the headspacing seemed ok. Still a mystery.

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Originally Posted by Peter Laidler

Just a couple of things - this has sort of whetted my appetite a bit in a strange way. I appreciate Joe's straight talkin' approach and the photos certainly show that there's plenty of meat in the case where the extractor slot is. I accept that if .303" brass ain't blowing out (and never has) then 762x54 steel should eaasily pass! But why. There's a simple answer coming up......

Djan.... I take the point and I agree about the cheapest ammo but when you go down that route, there is a chance that you will encounter a problem. And here it's a mechanical one. I don't agree that there ISN'T proper support because we've already shown/proved with 90% of the rounds and a lifetime of .303 rounds fired that even though there is an extractor slot, there definately IS proper support and the shell casings CAN support the load.

BUT......., some of them cannot support this. I would be finding the ammo type/make that WAS capable of supporting the load without splitting/rupturing and then concentrate on that ammo.

When you say 'the low spot' DJ, what do you mean? There are two 'low' spots on the rear face of a Bren barrel. The top 'low spot (1st and 4th photo) is to allow the slightly overhanging breech block feed horns a running clearance but clearly this isn't anything to do with your prob. Then there's a low part at the bottom of the barrel (2nd photo) the area of which is the cut-out that's causing the weak case to blow out. You can't do anything about this because it's the extractor way and the extractor on a Bren gun is a wonder of mechanical complexity because due to...... Do you want a slightly technical classroom lesson........ ? Anyway when the case is fully chambered and about to fire, the piston extension loosens its 'grip' on the extractor stay and loosens up the extractor on the about to be fired case.

Then after it's fired, the piston extension moves slightly rearwards and causes the extractor stay to REALLY tighten up on the case......... Now something else happens if you're following me....... The tight extractor is still gripping the red hot fired case as the breech block starts to drop down at the rear at commencement of unlocking and as it does, the lowest points at the face of the breect block violently rocks/rotates on the breech block stops in the gun body ( a major test by Armourers for worn guns) and the front rounded surface of the still tight extractor rocks on the extractor way in the barrel. The fired case is just gently rolled a gnats knacker to the rear and this gentle rolling motion just breaks the tight taper obturating seal of the case in the chamber. Now as the breech block has reached the unlocked point, it can move violently rearwards taking the loose case with it. In fact, it's SOOOOO violent, if the firing pin didn't punch a huge oval dish into the primer to swell it up and the ejector didn't additionally stake it in place to make sure, momentum would be freeing the primers out into the guns and causing jambs

That's why we rarely ever get ruptured cartridges in Bren guns. We DO of course but while the main extraction and ejection is violent, the actual PRIMARY extraction is a very quick, rolling leverage motion. That's why you can't weld up the hole or change the size to suit.

Sorry it's been a bit long winded...................

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SO... Peter - with all of this, are you saying that we are relying on the brass (or steel) of the casing to contain the explosion of a .30 cal round unsupported? What if I took pics of a round in the barrel with the bold locked on (or whatever you need) can you tell anything more from something like that?

Thanks,

I can't offer any more suggestions except to say that they don't blow out with any .303" guns and the mechanics of the design are the same with your 7.62x54 which ARE blowing out. What we DO know a couple of things. The first is that the steel case in some of the ammo you are using is insufficiently tough and malleable/elastic/flexible* to absorb the pressure without it exceeding the elasticity of the case at the point where it's got least support. When that happens there is a catastrophic failure that we see. The second and most obvious thing is that this catastrophic failure is caused by excess pressure

* trying to think of the proper engineering term there withoiut looking through Machinery's Handbook - but you get the point

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Originally Posted by djandj

Peter, thank you so much for the fantastic information. However, I still don't have an answer. The builder looked at my pics and said the headspacing looked right. IDK. My next thought is to send it to Troy and Barrelxchange as he does 54R conversions and let him look at it. He looked at the pics and also though the headspacing seemed ok. Still a mystery.[COLOR="black"]

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DJANDJ---

Unless you have some unique issue with the ammo, the case head is blowing out either because the solid part of the head is too short (unlikely if you are using the typical light ball), it is improperly head-spaced allowing the case to move rearward thus allowing the solid head of the case to move rearward then allowing the unsupported sides to be exposed to full pressure or the case is moving rearward because of the 1/2" delay issue I mentioned in my post above. For one or all of the above reasons the thin sides of the case are seeing full pressure while unsupported and blowing out. The higher pressure 54R is easily handled by the Bren mechanism and barrel but would be less tolerant to "loose" head-spacing than the .303 British round.

Do you know what headspace is ? IMO No one can tell if the headspace is correct from your pictures (see quote above) or any pictures unless they show headspace and feeler gages in use. You need a headspace gage, a set of feeler gages and the rifle in hand to check headspace.

IMO at this point you don't know if your rifle is head-spaced properly and everything I see indicates that it isn't either because of basic head-spacing or improper timing of the bolt opening sequence.

Good Luck solving your problem.


Joe

https://www.milsurps.com/images/impo...01dokceh-1.jpg

Does the Lahti LS 26/32 magazine feed reliably? How is it modified?

Vincent,

I believe the Mag in the pic is a ZB39 magazine (slightly beat up). I don't know of any Lahti LS 26/32 magazines that have been modified for use in a Bren.

Joe

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Originally Posted by Vincent

https://www.milsurps.com/images/impo...01dokceh-1.jpg

Does the Lahti LS 26/32 magazine feed reliably? How is it modified?

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That is a ZB 39 mag and yes it does. I can get about 20-25 rounds through w/o too much problem (when I am in a free state of course)

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Originally Posted by Joe H

Vincent,

I believe the Mag in the pic is a ZB39 magazine (slightly beat up). I don't know of any Lahti LS 26/32 magazines that have been modified for use in a Bren.

Joe

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Slightly beat up!!!! anyone think they can fix that?? It's blown up like a kernal of popcorn

Thanks Joe. I sent the barrel, bolt and a few rounds to Troy at BarrelXchange to check the headspacing.

I'd think he'd need the entire gun to check headspace. Your gun...

To be honest shooting 54r in a Bren is rather pointless. The ammo is not consistent, there are huge variations in lots and the "bodge" factor to save a few bucks on the ammo is pointless. If you're spending the 4k on a semi-Bren, feed it properly and it won't give you any problems.

I own three of the Historic Arms Semi-Bren's (Mk I , Mk II and an L4A3 ) and they run flawlessly on the proper diet of .303 and 7.62x51. If you want my advice, go back to .303, buy some good quality HXP or PPU modern ammo and enjoy yourself. The 54r is too dirty, corrosive and inconsistent for use in a semi-Bren.

https://www.facebook.com/video.php?v...32675541191352

The other problem with the "economy' conversion to 7.62 x 54, is that the Russian cartridge is actually more in the .30-06 class than .303 class.

And that is in its "rifle" loading.

Random lots of "unknown" MG fodder would be somewhat hotter, and would really make your eyes water if fired in a Model 38 or 44 Nagant Carbine..

Thus, even if the chamber "conversion" were done "properly", unless the gas port was reduced or the regulator "modified" (or replaced), the mechanism would be opening with considerable SPEED and violence.

The reverse is true with the Chinese conversions to 7.62 x 39, where, without some "creativity", the poor thing would be struggling to throw the bolt back far enough to feed and fire.

The Bren was, more-or-less, a Czech ZB-30 (7.92 x 57) REWORKED in a serious facility, to fire good old Mk 7 ball etc.

The Canadians built Brens in considerable numbers in 7.92 x 57 SPECIFICALLY for the Chinese.

The Taiwanese COMPLETELY re-engineered the design to run happily with .30-06! Now there is a desirable piece of kit!

Note to budding small-arms "designers": Build the gun AROUND the ammo!

Does anyone KNOW the certified, factory stated, manuafcturers stated, design spec CHS of this ammo - or even 7.62mm short come to that. Don't tell me saami or anything else UNcertified. What is the official design figure.

The UK MoD faced this problem when we were required to certify our live firing PKM's/Dragunovs/AK's etc etc. I tried to average out the 762x54 over about 15 PKM's and the differences were absolutely horrendous, varying by about (from memory) .031"............. But guess what? They all worked and over about 850 or so rounds, there were no problems. I never even bothered with AK's. Just stated that a .295" gauge must run freely.

BinO is correct in that it's the AMMO that is the weapon. All the gun has to do is to send it down to the target accurately and reliably

So I don't think that this 7.62x54Bren is suffering from CHS problems

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Originally Posted by browningautorifle

I'd think he'd need the entire gun to check headspace. Your gun...

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BAR is dead on. For the Bren you need the proper headspace gage but since the 54R is a rimmed case you can make due with an empty case and some shims and the correct headspace data. You also need the receiver with the barrel and locking shoulder installed and the 54r bolt without the extractor and some feeler gages .002" to .005".

Very simple to check.

Somewhere I read that Historic Firearms used some type of adjustable locking shoulder (LS) so that the gun could be easily head-spaced after the receiver was welded up. The LS was slotted so that the LS could be moved in its recess. Great idea but the friction of LS screw cannot take the force of bolt. The LS screw only holds the LS in place. If after head-spacing there was space between the rear of the LS and the LS recess in the receiver it would have to be shimmed, and I assume it was, so that the bolt force goes directly into the receiver. I've never seen one of their Brens so this is just conjecture on my part. Maybe an area to look into.

I built my own semi, its runs on 54r but I have to agree with csmarcher its certainly runs best on .303 British. You can find some good prices on 303 boxer primed brass cased ammo and reload to save money.

As Bruce noted the 54r is really a 30-06 class cartridge. The extra pressure doesn't seem to affect the semi since it has heavier recoiling parts. I still have to run on 3 or 4 gas setting.
C310 pilot recently posted about a friend's Bren Full Auto using 54r and it seemed to have gas related problems Bruce alluded to (too much gas).
Joe

One problem that used to manifest itself with Brens (and L4 guns) is that you'll NEVER get headspace if, when the breech block lifts up to lock, the outer top surfaces astride the cartridge recess (the areas outside and to the left and right) contact the barrel. The face of the breech block MUST NOT TOUCH the rear face of the barrel. This is called barrel clearance. If it does, it must be stoned down so that it is clear. Only the LOWER left and right surfaces of the breech block should touch anything, and they are the breech block stops.

The reason why the top outer surfaces of the breech block will occasionally touch the breech face of the barrel is when wear on the barrel seating face*, caused by fair wear and tear and hard use allows the tight barrel to intrude too far into the body.

If you think about it, CHS is gauged from the front face of the barrel rim seating (or chamber shoulder) to the breech block or bolt face. If some other part of the breech block/bolt face touches the face of the barrel, then no amount of locking shoulder changes will adjust that fixed gap!

We always check barrel clearance CHS with the breech block hand held in the gun body, less the extractor and stay. Only when the BBlock has been checked for barrel clearance and engagement or touching of the breech block stops will we check for CHS. And ONLY when the CHS had been adjusted/new locking shoulder will the breech block be put onto the piston extension and checked manually using finger pressure on the piston extension to close over the GO gauge. The breech block will NOT close over the NO GO gauge. IN THE CASE OF THE BREN, NOT CLOSE MEANS (while it might LOOK closed) THE PISTON POST CANNOT CONTACT THE FIRING PIN.

And when the BBlock is closed over the GO gauge, we want a further .002" feeler gap between the locking surface of the breech block and the locking shoulder!

I hope all that is a clear as mud. What is quite obvious is that some of the builders out there don't understand the mechanical complexities of setting these guns up

*that's the seating you see looking rearwards into the body when you remove the barrel and barrel nut. These could be re-bushed but only at factory FTR level

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Originally Posted by Peter Laidler

One problem that used to manifest itself with Brens (and L4 guns) is that you'll NEVER get headspace if, when the breech block lifts up to lock, the outer top surfaces astride the cartridge recess (the areas outside and to the left and right) contact the barrel. The face of the breech block MUST NOT TOUCH the rear face of the barrel. This is called barrel clearance. If it does, it must be stoned down so that it is clear. Only the LOWER left and right surfaces of the breech block should touch anything, and they are the breech block stops.

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Peter,
I encountered this exact issue welding up what is called a MGS demill here in the states into a semi. These are later demills and are very difficult to bring back to life. They are not done by the "professional semi builders" in the US. The front cut is through the barrel socket and the middle cut is through the locking shoulder. I found out the hard way that the front weld up affects the location of the breech block stops.

I had everything fitted up with a go gage and .002" between the rear of the breech block and the locking shoulder. I made one last check and realized the bolt was stopping on the breech block stops and not the gage. I had to grind the LS back for everything to fit up. I had inadvertently built in .030" additional headspace. The 54r would have definitely blown out. I ground the lugs back and had to make a new locking shoulder.

In retrospect it is very easy to check if you are just using the bolt, and receiver with LS in place and no extractor in the bolt. All springs removed.

Joe

Appreciate your comments Joe. Maybe one day I ought to write this technical spec up but it really is a subject taught over many weeks in a classroom with cutaway Brens on the bench etc etc

A "few bucks"??? 54R is .22 per round SHIPPED. Today's price for .303 = .70 per not counting shipping. I'd say at nearly 4 times cheaper, it's still worth fiddling with 54r. Multiple folks have managed to make this work so I don't see why I can't as well. Let's see what Troy says when he gets the parts.

Yeah! That’s why I want a 54R setup for my Bren. It’s not just a few bucks. At least it’s not to me.

Speaking of $$. Are there any good deals to be had on ZB39 magazines? $60 is a bit steep.

Is your Bren striker or hammer fired?

Quote:

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Originally Posted by Vincent

Yeah! That’s why I want a 54R setup for my Bren. It’s not just a few bucks. At least it’s not to me.

Speaking of $$. Are there any good deals to be had on ZB39 magazines? $60 is a bit steep.

Is your Bren striker or hammer fired?

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Sorry - no help with the ZB-39's I got mine many years ago. But 60.00 for a mag that size is still cheap when I'm paying 70-80 for a single 10 round HK45 mag.
My Bren is striker fired (I believe) as I haven't run into anything that looks like a hammer.

Why the need for ZB39 magazines? Is it something to do with the 762x54 ammo requirement or lack of 303 magazines? Just interested/puzzled

ZB39 mags are cheap in the UK at about £8-£10 each so $15 -$20

And so they might be (BP, thread 34).....,., but why the specific need? Is it something to do with being better for 762x54? Are they cheaper than 303 Bren mags with some 3.8 million being churned out

Joe H is the man to answer that question, Peter. IIRC, it’s something about the curvature of the magazine.

Ah, yes I remember the thread now...... Last few 762x54 jamb in a Bren mag. BIG problem if you were in a trench in Korea but not life threatening if you're shootin' a semi auto in your back garden.

Have a nice rest of the day. Warm and sunny here and I'm just assembling bren butt slides for pocket money!

Bren butt slides. Imagine that!:lol:

Quote:

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Originally Posted by Peter Laidler

And so they might be (BP, thread 34).....,., but why the specific need? Is it something to do with being better for 762x54? Are they cheaper than 303 Bren mags with some 3.8 million being churned out

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Yep - it's the curvature of the .303 mag and the rimmed 54R cartridge. If you try to stuff 54R into a .303 mag, you are only going to get 10 or 12 in there before the rimmed casing force the shells into a much steeper curve than the .303 mag has and you simply won't get that many in. And if you do, they will jam (and not necessarily on the last few in the mag.) Kind of sucks to have a 23 lb MG with a huge mag on top with only 10 rounds in it. So we use the ZP39 mags which have a different angle to them so we can get as many as 20 to 25 in them.

---------- Post added at 10:42 AM ---------- Previous post was at 10:41 AM ----------

Quote:

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Originally Posted by Brit plumber

ZB39 mags are cheap in the UK at about £8-£10 each so $15 -$20

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Great - you just let us know the website where we can order them then. Because Google knows nothing about it so far.

Quote:

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Originally Posted by djandj

Great - you just let us know the website where we can order them then. Because Google knows nothing about it so far.

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You could try these guys but not sure about shipping to US? GBP 39 for 5 in a carry case - M583 5 Rare WW2 ZB39 LMG Magazines - 08-Magazines & Loaders

Quote:

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Originally Posted by djandj

A "few bucks"??? 54R is .22 per round SHIPPED. Today's price for .303 = .70 per not counting shipping. I'd say at nearly 4 times cheaper, it's still worth fiddling with 54r.

---

But if the ammo is sh*t and you're having nothing but trouble, doesn't that defeat the purpose ?

I don't know about you, but my range time is somewhat limited. I want my guns to work, and work properly. Everytime i've run into a 54R Bren, or something converted to run what it wasn't originally designed for, it seems to me like a problem in the making. But hey ho, your gun, your time, your call.

:)

Many others have successfully converted their Brens to 54r. I have a 1919a4 converted to 54r and it runs perfectly. The first barrel the builder used also split the cases, but it did not cause stoppages like this barrel does. It is clearly something to do with the barrel or headspacing etc.

---------- Post added at 07:32 AM ---------- Previous post was at 07:32 AM ----------

Quote:

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Originally Posted by desperatedan

You could try these guys but not sure about shipping to US? GBP 39 for 5 in a carry case - M583 5 Rare WW2 ZB39 LMG Magazines - 08-Magazines & Loaders

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I just heard back from them. They WILL NOT ship ANYTHING to the US. I have no idea why. They did not elaborate.

I am more than convinced that it is an ammo batch problem Dan. Ignore me if I've said this before but what about trying some brass cased 762x54. I appreciate that steel is strong and tough (?) but there's steel - and there's steel. And you can be sure that the one-way-trip steel your cases are made of ain't gonna be good, believe me.

I appreciate that there's brass and there's brass too, but brass is very pliable and elastic. But the metallurgists here such as JM, Breaky and others that while the steel cases blow out and re-form slightly at the neck (in the recut chamber) it's supported while it does so. At the UN-supported extractor way, the steel blows. But not all steels......... some is as good as gold. You gotta find the batches that ain't going to blow

Quote:

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Originally Posted by desperatedan

You could try these guys but not sure about shipping to US? GBP 39 for 5 in a carry case - M583 5 Rare WW2 ZB39 LMG Magazines - 08-Magazines & Loaders

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Typically, from the ITAR/AECA regulations, import into the US requires prior approval via an approved ATF Form 6 Import Permit- this is not that hard to do as an individual, but requires a certain fondness for working you way through the ATF websites. You can download the required Form here:

http://www.atf.gov/files/forms/downl...-f-5330-3a.pdf

Notwithstanding the above, there is an extant exemption to the import regulations that permits INDIVIDUALS to import, on a "casual basis", things like this as long as the value does not exceed $100.00. That would appear to be the case here with these mags. The process is simple- as long they will ship it to you here in the US, just order them. If they get stopped in Customs, which is HIGHLY unlikely you will have to fill out a Declaration Form indicating value, personal use, etc.

-TomH

ON that basis, needy US owners might contact a UK forumer and come to some agreement. Such as having a few shipped to a UK address and just shipped onwards for the price of a jiffy bag! Small packet rate is fairly reasonable and just needs a stick-on CN22 declaration.

Quote:

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Originally Posted by Peter Laidler

I am more than convinced that it is an ammo batch problem Dan. Ignore me if I've said this before but what about trying some brass cased 762x54. I appreciate that steel is strong and tough (?) but there's steel - and there's steel. And you can be sure that the one-way-trip steel your cases are made of ain't gonna be good, believe me.

I appreciate that there's brass and there's brass too, but brass is very pliable and elastic. But the metallurgists here such as JM, Breaky and others that while the steel cases blow out and re-form slightly at the neck (in the recut chamber) it's supported while it does so. At the UN-supported extractor way, the steel blows. But not all steels......... some is as good as gold. You gotta find the batches that ain't going to blow

---

Peter - you may be right. As I mentioned I have over 100 rounds shoot perfectly well through that gun and barrel. However, the disturbing part is that spam cans are fungible. It's not like I can say "just don't by brand X ammo" etc. I was shooting regular old Russian 147 light ball. The rounds are indistinguishable from one another. The only thing I have on the can at this point is D64 on the bottom. That doesn't tell me much. But if Troy says the barrel is cut right and good to go, I will pop open the next spam can and pray. (and report back for all of you)

OK so now the "explosive update" I got the rifle back from Troy who very kindly agreed to re-ream the barrel for me. I used a DIFFERENT spam can of 54R. (see pic) Fired 60 round FLAWLESSLY (no case fatigue at all) then.... on the first round of a fresh mag. BOOM!!!! The case failed on BOTH sides (see pic) and blew the mag out of the rifle!!!!. The Builder claims it's and "ammo issue" and won't help. (of course he build the damn thing with the express purpose of shooting Russian steel cased surplus ammo....but that's another issue).

So.... gang, I'm on my own with this thing. Need ideas. How does the rifle cycle 60 times perfectly and then have a catastrophic failure like this! Again, seems clear that the cartridge is unsupported in two places where the barrel is beveled in the back so... does head spacing matter when the casing is unsupported on the sides no matter how close the rim of the case sits? Keep in mind that when he first sent the rifle to me the first barrel caused every cartridge to blow out, but for whatever reason, the gas pressure was never enough to blow up the mag. When I got it back, the new barrel (or combination of barrel and rifle) now causes a BOOM ever 60 rounds or so.

At least he seems to have fixed the recoil spring issue. I cycles fine, but does have the LITTLE problem. We need to resolve. Can't expect any casing to withstand the pressure without the support of the barren or other mechanism.

Thanks for the help. I'm on my own and don't build guns myself so....... All help/ideas are welcomed.

SEE PICS BELOW
https://www.milsurps.com/images/impo...gpzxgthg-1.jpg
https://www.milsurps.com/images/impo...otjsdbzp-1.jpg
https://www.milsurps.com/images/impo...nqjesdov-1.jpg

Quote:

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Originally Posted by djandj

so... does head spacing matter when the casing is unsupported on the sides no matter how close the rim of the case sits?

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Djandj,

I know I can't give you any new advice. In one respect or another your problem is "head-spacing". You comment above indicates you don't understand the problem. Both TactAdv and I told you Troy wasn't going to solve your problem since you only sent him the barrel and consequently he couldn't check for a headspace problem.

IMO it's one of three problems:

1 - Head-spacing is too loose. It may work for .303 but I doubt the 7.62x54R is as tolerant as the British round. The 7.62 only has to move a very small amount for the pressure to see the thin wall od the case.

2- Timing is off so that the bolt is opening too early allowing too much pressure on the case as it extracts.

3-The bolt is hitting the two lugs on the receiver before it closes on the cartridge. Could happen but not as likely as the two above.

Here is some relevant reading material:

Login

Headspace 101 for .303s in The Lee Enfield Forum Forum

Login

The Bren can be checked for headspace with practically no tools or gages. More to follow.

Joe

Djandj,

Here is a simple way to check headspace on a Bren. The rim thickness on the 7.62 is .063" so you can use the same headspace dimensions as the .303. The Bren was never designed for the 7.62x54r so I'd keep the headspace as low as possible.

Strip the frame, carrier and bolt. Remove the firing pin and extractor from the bolt. Take a properly resized MT case or unfired 7.62x54r case with the powder and bullet removed. The 7.62 x 54r is within .001" of the .303 british rim so you can check using the .303 headspace dimensions. Check the rim thickness. It should be about .063". It is a little difficult to check since the head is not flat. Glue on a .003- .004" piece of shim stock on the head of the case. Slide the case in the barrel. Now only install the bolt without extractor, no carrier spings etc, only the Bolt. Push it into the locked position. Push the bolt forward with your finger. The case should be snug under the bolt. If it isn't check Item 3 above. With your finger still pushing on the bolt and using a feeler gage you should have between .002" and .005" between the bolt and locking shoulder. If its .010" or better you may have problems. If its .015" plus IMO you definitely will have a problem. You probably will have to replace the locking shoulder with a longer one.

Every time the bolt closes the relationship of the carrier and bolt should be as in the attached pic. The carrier should have to travel 3/8" to 1/2" before the bolt unlocks. If you don't you may have problem 2 above.

The second pic shows the gap between the bolt and locking shoulder on a Bren that was having the same problems as you.

Joe

Joe - THANK YOU for your help (and patience with me). If that is the EASY way to check headspacing, I'd hate to see the hard way. That operation just assumes I have .0003 shim stock and a feeler gauge just laying around. (as I said, I'm not a metal worker or gunsmith.) I understand headspacing as it applies to my 1919a4 for example. The distance from the end of the barrel to the bolt face. However, when the barrel has huge cut outs on it (exactly where the cases are blowing out) I don't see you can ever make the headspacing tight enough to matter.) Again, I don't know. I followed your directions as best I could and took pics. Not sure it helps. (see attached) I suspect that I can send it to someone to get the headspacing checked.

Question: what are the "locking shoulders" everyone keeps talking about? And what is movable in the receiver to change the headspacing anyway?
Last observation, your second hypothesis (i.e. that the gun is out of timing- makes logical sense as it does appear that the bolt may be moving back before the pressure has dropped to a safe level.) Can this happen only once after 60 rounds or so? (B/C that is when it happens). What can we do if the rifle is mistimed?

Again, thanks for all the help. I very much appreciate it.

https://www.milsurps.com/images/impo...2xg7akgh-1.jpg
https://www.milsurps.com/images/impo...wcskoioj-1.jpg

OK Disregard the locking shoulders question. Figured out what they are. I certainly don't appear to have the gap Joe was talking about and showed in his pic. Of course I don't have a feeler gauge either.

Feeler Gauges should be readily available from Auto tools & Accessories stores. Also good hand tool retail & trade outlets.

If I can just chip-in here for a second......... The FIRST thing you MUST do is get down to Brian at BDL and get the little SAS booklet about the Bren. It's important that we are all on the same wave-length when it comes to the names and identity of parts - such as the locking shoulders.

The SECOND thing you ought to ask is this. What EXACTLY is the CHS spec for soviet 7.62 x54R. I was resonsible for certifying that the regularly used foreign weapons were '....certified fit to fire by a current and competent authority' - me! Trying to find out the bore gauge size and CHS was virtually impossible as it had to be the weapon or ammo manufacturers specification. And manufacturers spec isn't the SAAMI or proof house or uncle Tom Cobbley or some of the figures bandied about or........ You get my drift. So I used to write out a well tried and tested format while certifying a weapon fit to fire. So that's the first tying you need to know - the certified CHS.

As for what you call 'the timing' during the unlocking phase. From the pictures and description it's not clear whether the unlocking system in your gun is still by means of the unlocking cam part of the piston post acting to draw down the rear of the breech block. If it is, then the timing cannot (?) be out. This is because - and I'll keep it very technically simple - the dynamic and engineering geometry is such that once the bullet has passed the gas port, the gas MUST impart sufficient energy to move the heavy piston, piston extension, piston post etc etc (the PPE) .5" just to reach the point at which COMMENCEMENT TO UNLOCK starts. In simple mathematical terms, by the time the PPE has moved this .5", the bullet has moved 30" - or 2'6" and it's well clear of the barrel. But there's more..........

There is some discussion as to exactly when the gas pressure in the barrel returns to neutral/atmospheric. Some say it's 6" after the bullet has left the bore. Others, like me say that at 1" (or 3" if the flash eliminator is fitted) the gas pressure is at a safe working load. So given that the PPE has to move at least 1" to fully open/unlock the breecch block, during which time the bullet will have moved 60" past the gas port there is an inbuilt and infallible mechanical safety during your guns unlocking phase.

Peter,

Regarding your comments on "timing". You have the experience with the Full Auto Bren of which I have none. The striker semi auto version, which djandj has operates somewhat differently. In the full auto Bren the return spring drives the full mass of the carrier, piston and bolt forward to close the bolt and fire the round. In the semi version the bolt must be closed separately then the striker is released by the trigger to fire the round. The same return spring must now move the bolt, carrier and striker(additional mass) forward and cock the added striker spring. The stroke is now shorter due to the presence of the striker behind the bolt and carrier. The return spring cannot be compressed to its original design compression. This can be alleviated by adding a plug equal to the length of the striker behind the return spring. I don't known if this was done in djanj's Bren.

My own observations in building a semi Bren are that due to welding the receiver together and the spring issues mentioned above it is possible that the carrier does not travel freely and does not return to the position indicated in the pic I posted above allowing a shorter or no travel before the bolt unlocks. The lower part of the striker in a semi normally is the same x-section as the carrier and runs in the same grooves behind the carrier. A tab extends above the lower section which strikes the firing pin. The upper tab is many times flush with the front of the striker allowing the rifle to be fired if the carrier is short of the correct "in battery" position. If the tab is located 3/8" behind the front of the lower part of the striker then if the carrier is not fully forward the lower striker will hit the carrier and not fire. I don't know if this safety feature is built into djandj's bren. Most of the semi's I have seen do not have this feature.

I couldn't find any headspace data on the 7.62x54r. Pressure would not be an issue with Bren but I'm not sure how relevant a "Field" gage measure would be since it was never meant to be used in the Bren barrel. The conversion has been successfully used by USA semi Bren builders. It works in my Bren which has very tight headspace. You can see from the pic below which I previously posted that there is little margin for error due to the depth of the solid base of the 7.62x 54 rounds. The .303 round has a much deeper base and consequently more tolerant of loose headspace.

IMO this why some people experience no problems with .303 British in their semis but start having problems with the 7.62x54R.

Joe

I'm going to the US next month or so, so will arrange with Brian that I can see one. I appreciate that it is difficult for me here even picturing the mechanics of a semi auto Bren there. But it's a credit to the semi-designers for their work. Me, I'd just stick to .303"

OK Guys. Feeler gauges ordered. I will try to get an accurate measure of the headspacing so we can start there. After that, it has been hypothesized by Troy at Barrel Works that since the gun tends to go BOOM on the first round of the mag each time that it could not be fully locked up when it fires. (IDK) He had suggested looking at the extractor and making sure that it wasn't getting in the way of a solid lock up. Who knows? But head spacing measure first. I will then report back.

Thanks again all.

I don't have any semi-auto Bren guns here. My two guns are both restricted, post sample originals. There may be some to look at in PA. Wiselite Arms was there last time, (set up directly behind me in fact), which would be nice because they did a much better job than Historical Arms IMHO. They had them in 7.62x54R too if memory serves. I don't know if they're still building them or not since that was five years ago.

Brian:

If you wish... I can send one of mine for you to test drive while your entertaining guests... just let me know.

ATB

Gery Hackney

Brian, I agree that Wise Lite Arms did a better job. Their semi setup is different and better IMO. But the big difference is the quality of their receivers.

They stopped selling Brens a while back, but they still have a receiver weld service and a repair service.

Quote:

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Originally Posted by Brian Dick

I don't have any semi-auto Bren guns here. My two guns are both restricted, post sample originals. There may be some to look at in PA. Wiselite Arms was there last time, (set up directly behind me in fact), which would be nice because they did a much better job than Historical Arms IMHO. They had them in 7.62x54R too if memory serves. I don't know if they're still building them or not since that was five years ago.

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Brian,
Where in Pa? I'm in Western Pa near Pittsburgh.
Joe

Quote:

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Originally Posted by djandj

All help/ideas are welcomed

---

I only that I had the pleasure of firing one once but just as a novice can it be a timing issue that the case has started to move with the breech assembly whilst the projectile is still in the barrel and not clear of the gas port which will obviously relieve the internal pressure. You would not notice this until the case ruptured, then again 60 rounds prior to that no incident, so is it the ammo given the copious quantities Russia produces (Lot No. ?) there is a Bren barrel brand new for sale on usedguns.com.au but it is very expensive and you probably would not get it out of this country...just trying to assist with some obtuse thinking

Postscript ~I got to thinking about the timing and the rupture and copied the Pic from page one and it looks like a drag mark from a rim on the cartridge soooo my theory is that if it happens on the first stripped round under the tension of 20-24 rounds behind it then it may slow the carrier down just that tad. Now going on what has been said that some of the semi auto versions may not have a a built in safety device to stop a slam fire could the striker drop and fire the round before it is all locked in the chamber. The timing gap you would not notice before it all went bang and the mag flew off.... what say others ?

Joe H stated about semi auto Bren's

The upper tab is many times flush with the front of the striker allowing the rifle to be fired if the carrier is short of the correct "in battery" position. If the tab is located 3/8" behind the front of the lower part of the striker then if the carrier is not fully forward the lower striker will hit the carrier and not fire. I don't know if this safety feature is built into djandj's bren. Most of the semi's I have seen do not have this feature.

What happens if you only load 29 rounds instead of 30 in each magazine?

Here’s why I am asking. Every time the bolt moves back it lifts all the rounds in the magazine.

With these closed bolt setups and a full magazine the bolt is lifting all 30 rounds when it’s pulled back to load the first round.

Is it possible that there is not enough room in the magazine for the rounds to be lifted when it’s full and the first round is being damaged by the bolt as it is pulled back?

You could eject the first round from a full magazine and inspect it.

On a semi, what stops the firer releasing the striker onto an unlocked breech? Obviously on a normal Bren this could never happen but a semi? Thinking along the same lines as Vincent above, the extra drag of a full mag may be slowing the carrier down and it doesn't lock up correctly.

Quote:

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Originally Posted by djandj

OK Guys. Feeler gauges ordered. I will try to get an accurate measure of the headspacing so we can start there. After that, it has been hypothesized by Troy at Barrel Works that since the gun tends to go BOOM on the first round of the mag each time that it could not be fully locked up when it fires. (IDK) He had suggested looking at the extractor and making sure that it wasn't getting in the way of a solid lock up. Who knows? But head spacing measure first. I will then report back.

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djandj,

Magazine issues???

The first link I referred djandj to and I posted previously above had this reply that I posted on The Weapons Guild Forum in 2012. It was about the same problem of 7.62 cases rupturing at the base.

QUOTE "From my experience the mag was overloaded. Other guys may find it different but until I got my ZB 39 mags altered they were popping out and jamming. It sounds like the round was jammed and went off before the bolt was locked or it would be my first guess the the overloaded mag and consequent drag on the bolt prevented the carrier from going fully forward and just barely locking but not fully forward so that the pressure was not low enough for the bolt to open causing the split. On the Bren the carrier has to move about a 1/2" before the bolt unlocks to allow the bullet to clear the barrel and the pressure to drop.

Did you modify the striker so that it couldn't fire unless the carrier was fully forward?" QUOTE

There is plenty of space in the ZB39 mag, which I assume you are using, for the bolt to push the rounds up into the mag as the bolt is pulled back. The ZB39 mag with a capacity of 25 rds was designed for the 8x56R, a rimmed round similar to the 7.62x54r. You can only get 15 to 20 rds max of 7.62x54R into an unmodified ZB39 mag. At 20 rds its not the spring tension that limits the capacity its the fact that the curvature of the ZB mag does not fit the 7.62 rd. The geometry of the two cases is different. As you get close to 7.62 capacity (15-20rds) the tips of the cartridges start to dip into the mag eventually stopping on the forward lip of the mag. This is what limits the capacity of the ZB-39 mag using the 7.62x54R. I've found using 7.62 x 54R dummy rounds that as you get close to "capacity" the tip of the bullet starts to hit the forward lip of the mag. This steals energy from the closing bolt possibly causing the carrier not to close in the full forward position. The rounds would cycle but I could see the damage to the tip of the bullet hitting the forward lip of the magazine as it cycled into the chamber.

Brit is exactly correct in that the carrier of a FA Bren must be in the full forward position "in battery" for the gun to fire. In the pic below an open bolt FA cannot fire unless the rear of the carrier is in Position A in the pic below. The piston post which fires the round and is attached to the carrier cannot contact the firing pin until the carrier reaches Position A.
In the striker- fired semi Bren if for whatever reason, mag drag etc., the rear of the carrier only reaches Position B and the striker tab is flush with the face of the lower part of the striker (typical of many striker fired semi Brens) then gun will fire with the rear of the carrier in Postion B probably allowing the bolt to open too soon with pressure on the cartridge causing the problems djandj is experiencing.

Prior to my 2012 reply (above) I realized the typical striker fired semi could fire out of battery. I redesigned my strikers with an offset between the tab and the face of the lower section so if the carrier was in Position B the lower part of the striker would hit the carrier and the tab would not contact the firing pin.

Joe

All,

Below are pics of how I altered the semi striker so that the rifle could not be fired "out of battery". These are pics of my rough prototypes to show how it works. The second pic shows the set up at the instant of firing. The length of the firing pin and tab offset have to be coordinated so that tab cannot hit the FP unless the carrier is in the full forward position. About 1/4" must be left clear to the rear of the tab so that the recoil buffer will work.

Joe

Quote:

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Originally Posted by djandj

That is a ZB 39 mag and yes it does. I can get about 20-25 rounds through w/o too much problem (when I am in a free state of course)

---------- Post added at 04:39 PM ---------- Previous post was at 04:34 PM ----------



Slightly beat up!!!! anyone think they can fix that?? It's blown up like a kernal of popcorn

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Djandj,

I re-read this thread from the beginning. I found the quote above. There is no way 25 rds of 7.62x54R will feed correctly through an unmodified ZB39 mag in a Bren. Yes you can stuff them in an unmodified mag but they will not free freely into the chamber. In my experience 20 rds is the ultimate limit unless the magazine has been modified which takes some doing for 25 rds of 7.62 x 54R.

Try 10 -15rds in the mag and very possibly your problem will go away if the rifle is head-spaced properly. You should also check out the striker "out of battery" issue.

Joe

Harrisburg, PA.

That is an ingenious way of ensuring that the gun cannot fire unless the breech is fuloly closed Joe. Is that your invention or the standard semi-auto norm? The hammer part of your hammer block is acting the same way as the hammer part or what we call the 'hammer face' of the piston post in a standard gun. The piston post and your hammer cannot hit the striker with sufficient force unless the breech block is fully closed/locked. It gets better too because even if the breech block isn't fully closed in your method (or the standard piston post method0 and you decide to close it manually somehow, it still won't fire due to insufficient energy remaining within the hammer to initiate the primer.

I know it's a bit anorakish but keep thinking to myself that if we could get 6 or so UK and US/Can et al Bren forumers together in a classroom together with a few scrap Brens, paper pencils and a black-board we could solve this problem in an afternoon and all go for a beer in the evening. Are you game Tankie and Skippy........, between us we've fixed a zillion of them - and know them inside out!

Peter,

I started building my first Bren semi in 2008. I bought the striker from one of the "Professional Bren Builders" . The upper tab was flush with the face. I began to get concerned that the design really had no way to prevent out of battery discharge. No one seemed to have any problems nor did I with .303 British and standard .303 Bren mags. As people began to build and convert to 7.62 x 54r a few problems like Djandj's began to appear. Most could easily be traced to loose headspace but a few indicated problems with the carrier not closing properly. I became more concerned and in 2011 reconfigured my strikers as shown above. I posted my ideas on The Weapons Guild Forum. I don't know if anybody used my idea or not or if somebody else had already thought of it and was using it unknown to me. There are more than one design variations around. There is another type of striker design which could be on djandj's Bren (can't tell from his pics) that utilizes a striker spring that is not on the return rod and eliminates the buffer which may have the proper out of battery safeguards. There also is a hammer fired variation. The one I built was the typical design used by most individual builders.

"Professional" Semi Bren building is pretty much a cottage industry here in the States with a number of us individuals building our own. As you are probably aware there never has been any testing done to any real extent on the semi designs. Nothing like the 100,000's of rounds and years of design that went into the original ZB/ Bren design. I for one am totally impressed with the Bren design and I'm happy to a least have working semi-autos.

Joe

Attachment 62355

The striker is from another Historic Arms Bren with issues.

The actual un-machined block looks too light to be reliable Vince - although I'm just saying how it looks from here of course. I think that I would hollow out that block and weight it with molten lead to give it more inertia to do its job. But it's all making a bit of sense now. You game to solve the 7.62 x54R bren problem once and for all Vince......? Followed by a few beers?

Quote:

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Originally Posted by Vincent

Attachment 62355

The striker is from another Historic Arms Bren with issues.

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Vincent,

What are the issues? 7.62x54R like Djandj's.

Where does the striker spring go. Is it on the return rod or is it a separate spring & rod that bears on the upper striker tab. There is an offset between the upper tab and the face of the lower section but since the upper section is the full width of the striker it's hard to see exactly where upper section hits the FP. It looks like it can't go past the upper projection of the bolt just hitting the FP.

I notice that there are no lands on your striker or on the carrier (see comparison below). The original carrier has lands that run in the grooves in the receiver. I read a write up on HA that indicated that they removed the lands and grooves from one side of the receiver. Are there lands on the other side of the striker & carrier?

Without having the gun in hand it's hard to comment why yours has issues. HA has been
building semi Brens for quite awhile so it's hard to find a flaw, if any, just by looking at parts. Have you questioned Historic Arms about the issues?

Joe

Quote:

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Originally Posted by Peter Laidler

The actual un-machined block looks too light to be reliable Vince - although I'm just saying how it looks from here of course. I think that I would hollow out that block and weight it with molten lead to give it more inertia to do its job. But it's all making a bit of sense now. You game to solve the 7.62 x54R bren problem once and for all Vince......? Followed by a few beers?

---

.....after a few beers in the shop, I'm thinking you pour it full of solid gold. Or DU. ;-)

-TomH

DU....... there's a thought!

Quote:

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You game to solve the 7.62 x54R bren problem once and for all Vince......? Followed by a few beers?

---

I am game, Peter. Double game for the beers.

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Joe,

The picture is from this thread Anyone have a Wise lite arms Bren it’s on the second page, but some of the posts on the first page are worth reading.

The striker and carrier design used by Historic Arms does not have a left hand side key/land. This feature is part of his denial of full auto parts modifications. The left channels of the receiver are filled with several weld plugs and made flush. The other side of the striker shown in the picture has the key/land machined into the side. As to insufficient inertia... the design uses a very large compression spring which seats into a pocket milled into the rear of the striker and passes over the center recoil rod and terminates against the rear slide wall. Oddly, to maximize the size of the striker spring... but still have enough room for its recoil compressed form - Historic Arms removes all of the slide buffer parts and has the striker spring seat in the pocket that remains after their removal. I've never had a failure to fire for lack of striker force and the extra striker spring seems to compensate for some of the missing buffers recoil absorption. I have not yet crushed a striker spring or battered the slide face.

Quote:

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Originally Posted by Peter Laidler

The actual un-machined block looks too light to be reliable Vince - although I'm just saying how it looks from here of course. I think that I would hollow out that block and weight it with molten lead to give it more inertia to do its job. But it's all making a bit of sense now. You game to solve the 7.62 x54R bren problem once and for all Vince......? Followed by a few beers?

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Hey guys, I'd be happy if you could just solve MY 54R problem, much less all of them (lol) And I'd be buying better than beers.

---------- Post added at 09:20 PM ---------- Previous post was at 09:19 PM ----------

Quote:

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Originally Posted by Vincent

Attachment 62355

The striker is from another Historic Arms Bren with issues.

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Funny, my Historic Arms internals don't look like that. A bit different.

---------- Post added at 09:29 PM ---------- Previous post was at 09:20 PM ----------

Quote:

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Originally Posted by Joe H

All,

Below are pics of how I altered the semi striker so that the rifle could not be fired "out of battery". These are pics of my rough prototypes to show how it works. The second pic shows the set up at the instant of firing. The length of the firing pin and tab offset have to be coordinated so that tab cannot hit the FP unless the carrier is in the full forward position. About 1/4" must be left clear to the rear of the tab so that the recoil buffer will work.

Joe

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WOW Joe - you are way ahead of me on that. Yes, the gun does blow up usually on the first round of the mag (after manual racking). However, here in CA I can only put 10 round in the mag at a time. I have a wooden dowel in there to take up the rest of the room. Here are some more pics of my innards for you.

https://www.milsurps.com/images/impo...xkkikysz-1.jpg
https://www.milsurps.com/images/impo...lfte0dvh-1.jpg

But from the damage to the casing (and the mag) I keep thinking that it fired out of battery or something like that. But usually only one out of 60 rounds.

The biggest problem is crap 54R ammo.

I've mentioned this before, and I'll say it again, the semi Bren and the full auto Bren run wonderfully on .303 and the L4 series run wonderfully in 7.62x51, so with all due respect I can't see the point in wasting range time trying to reinvent the wheel.

I know there is a fellow on another forum who's been having all sorts of trouble with a Browning 1919A4 while trying to get it to run on 54r and has been told the same thing. Stop wasting your time......

Just because something is cheap (54R ammo for example) doesn't mean its any good.

I've had several of the Historic Arms Bren's through my hands in both 303 and 308, and they all have functioned flawlessly.

Gary

Yet another few succinct words of wisdom from the CSM that I'm sure we all agree with. I know I always sing the praises of the ferocious 762x54R PKM but it was made and designed with that rounbd in mind - even poorly, cheaply made stuff. And the round is fully supported in the breech. Not so in the Bren of course

Thanks Wally G for the info on the inertia available (thread 77)

Peter,

I'll drink to your proposal but it might take me a little while to get to your favorite pub :D .

Vincent,

That link to 1919a4 was great. I read about the HA Bren in Small Arms Review. Everything was wonderful. Wiselite and head-spacing OMG. When I first decided to build semi Bren I found a tutorial by "Pirate", another so-called professional builder. At that time the IO cut receivers were available so that there was one cut to weld between the locking shoulder and the barrel socket. He, probably like Wiselite, set up the weld by fitting the magazine, not setting the headspace:eek:. I couldn't believe it. I set the headspace first then checked the mag fit. If the mag didn't fit then there was something very wrong.

Wally G.

Thanks for your details of the HA build. I had read about what Len had to go through to meet ATF specs. The latest ATF approval letters are far less restrictive.

Gary,

Yes my Brens run better on .303, but they also run without any problems on 54R. If you are building your own and are willing to take care of all the small details they can be made to work with 54R both semi and FA (see post from C310 pilot about FA 54R Bren). The details being headspace, timing and the magazine. The ZB39 mag was not made for the 54R round and although it can be made to feed that doesn't mean it will work properly without modifications. There are no other reasonable magazine options.
For most people what I stated above is not the case.
My 2 cents

Djandj,

It's impossible to tell how the wood plug affects mag capacity and feeding. As far as I know this issue has never come up. I guess there are not many people with Brens in California.

Joe

Quote:

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I know I always sing the praises of the ferocious 762x54R PKM……..

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I wish you would stop doing that, Peter. Then I could stop kicking myself in the a** for passing up a really good deal on one. What was I thinking! :banghead: :banghead:

We had a tacit sort of agreed standard to restrict Bren magazines to 10 rounds dating back to the 50's or so. Only seen a couple of them including one that was in the 'shooting cupboard' of my sons old school Cadet Force. It had a steel plate brazed through the square section that extends out of the back of the magazine (the part that had the mag catch lug), positioned so that the mag platform could NOT be depressed past 10 rounds capacity.

You could insert and remove the platform for assembly and cleaning but only with a bit if jiggling with it hanging on the spring. Once past the 'blockage', it was OK. Didn't affect the free passage of the spring because the spring doesn't intrude into the rear boxy section. I took it into Warminster. Anyone interested and I'll see if it's still there and photograph it. But pretty foolproof. Used by recruits during their initial live firing so thet don't get tooooo carried away - as you are prone to do!

To be honest Vince, id'd be hard pushed to make a decisioin over a PKM and an L7/GPMG. But if it was heart rule head time, it'd be GPMG. Anything else, the PKM

Quote:

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Originally Posted by csmarcher

The biggest problem is crap 54R ammo.

I've mentioned this before, and I'll say it again, the semi Bren and the full auto Bren run wonderfully on .303 and the L4 series run wonderfully in 7.62x51, so with all due respect I can't see the point in wasting range time trying to reinvent the wheel.

I know there is a fellow on another forum who's been having all sorts of trouble with a Browning 1919A4 while trying to get it to run on 54r and has been told the same thing. Stop wasting your time......

Just because something is cheap (54R ammo for example) doesn't mean its any good.

I've had several of the Historic Arms Bren's through my hands in both 303 and 308, and they all have functioned flawlessly.

Gary

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With all due respect CS, my 1919a4 runs like a Swiss watch on 54R (Thanks to Troy at BarrelXchange). As for the Bren. Len BUILT IT WITH THE SPECIFIC INTENT TO SHOOT SURPLUS 54R! Why else would you convert a .303 to shoot the equally expensive (if non-surplus) 54R? Why convert it at all? Well, .303 is .70 per and drying up fast. 54R is .22 per round SHIPPED. As for being "crap" I don't see it. If you look at the steel casing that burst, they were pretty thick. That much steel will be far more tough than a comparable brass round. So? I don't know. Others have said that they have got their Brens to run on 54R. I'd like to do the same.

We can all see the frustration and the point you're making DJ but the simple and irrefutable FACT is that your particular gun is causing the case/cases to blow out at the point at which they are at their weakest and unsupported. At the cutout for the extractor. Your BRowning doesn't have this feature and that's why they ain't blowing out. The 7.62mm L4 barrels don't have this feature either and they don't blow out either.

Line 4 of your comment, you forget that while the steel case is tougher (? in metallurgical terms) than the equavelent brass case, the brass has several additional properties including its pliability and resiliance. THAT's why it is so good at obturating the chamber among other things of course.......

Quote:

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obturating

That stops or plugs up; used in closing or stopping up: specifically applied to a primer for exploding the charge of powder in a cannon, and at the same time closing the vent, thus preventing the rush of gas through it in firing.

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Being a layman, I had to look it up. :thup:

Quote:

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Originally Posted by Peter Laidler

We can all see the frustration and the point you're making DJ but the simple and irrefutable FACT is that your particular gun is causing the case/cases to blow out at the point at which they are at their weakest and unsupported. At the cutout for the extractor. Your BRowning doesn't have this feature and that's why they ain't blowing out. The 7.62mm L4 barrels don't have this feature either and they don't blow out either.

Line 4 of your comment, you forget that while the steel case is tougher (? in metallurgical terms) than the equavelent brass case, the brass has several additional properties including its pliability and resiliance. THAT's why it is so good at obturating the chamber among other things of course.......

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Yes Peter, quite true that the 1919 has a flatter barrel end and doesn't leave parts of the round unsupported (why in the world the Bren does that IDK). But I brought it up only b/c CS had mentioned another 54R Browning not working. Again, others seem to have managed to make the 54R thing work in a Bren so I can't see why I can't as well. Once I check the headspacing, it will be one less thing to question. After that I'm open for ideas. After all, the rifle fires 60 rounds flawlessly prior to BOOM.

Ah, yes, that's the point we raised a few threads ago....... 60 rounds flawlessly tells me that the support within those 60 rounds is marginal at the weak point. But every so often a case comes through that is slightly thinner or maybe there's a slight increase in pressure or..... and then a catostrophic failure occurs as we see.

I wonder if you could just borrow 2 mags worth of factory brass cased ammo and see what happens. I appreciate that this isn't quite what you should be doing but it's a good start when you're trouble shooting - if you'll excuse the pun!

My friend fires this cheap as chips steel cased 762x54 stuff in a slightly modified Vickers and it sings like a train........... It even fire-forms the front of the neck into the old .303" chamber contour without a wimper too. But at that end of the case, it's thin material and more forgiving.

Djandj,

This, I know is extremely frustrating to you. As Peter mentioned earlier,if a group familiar with the Bren could get together and actually handle your rifle I think the problem could be found. You are admittedly not a gunsmith and probably not at all familiar, at least until now, with the workings of the Bren gun.

Over on the Weapons Guild (you may want to inquire over there as most of the participants are semi builders and some may have had the same issues) many of the builders have used the 54R conversion successfully and ones who posted about problems could trace them back to some sort of head-spacing issue. Csmarcher indicated that he had run a HA .308 Bren flawlessly. The barrels, I'm almost certain, HA provided were SA 7.62 x 51, not L4 barrels which are pretty much unavailable in the US. The SA barrels have the same notch as the .303 British. I have a SA 7.62 x 51 barrel and a .303 barrel converted to 8 mm Mauser. I did the same analysis that I previously posted for these two calibers by splitting the heads to be sure the solid end of the case extended past the notch for the extractor, which they did.

In addition to Peter's suggestion maybe try not using the Mag and see if any problems arise. To check to be certain your rifle can only fire with the carrier in the proper position, take a primed cartridge with the bullet and powder removed and place it in the chamber. Drop the bolt on it. Slowly withdraw the carrier/bolt until the carrier is on the verge of unlocking the bolt. Now ease the bolt toward open and try to hold the carrier in the rear position, just about to unlock, Position B in my previous illustration. Pull the trigger. If it fires the primer something may be preventing the carrier from fully locking the bolt. If it doesn't fire try again with the carrier half way to locked position. You may have to remove the return spring for the test. Of course the striker spring has to stay in place. If I had your gun I'd check headspace first then do this test. If it headspaces ok and fails this test I'd be trying to find out why carrier is not returning consistently to fully locked position.

IMO either the headspace is too loose for the 54R or for whatever reason it is intermittently able to fire out of battery or at least not fully locked up. Drag on the return cycle, possibly a mag issue. Other than that I'm out of suggestions :confused:

Joe

Quote:

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Originally Posted by Joe H

Csmarcher indicated that he had run a HA .308 Bren flawlessly. The barrels, I'm almost certain, HA provided were SA 7.62 x 51, not L4 barrels which are pretty much unavailable in the US.

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Joe

I'm actually a very lucky chap and have TWO L4 barrels for my L4A3 that Len built. I actually managed to obtain a "Bren Conversion Kit" back in the late 80's from IMA which came with an L4 Barrel, 7.62mm Breech Block, L4 Mag catch and ejector housing and instructions....

From that Len was able to build a true L4 series gun for me on an Inglis Mk II reciever.
I found the 2nd barrel on Gunbroker in a mixed lot of Bren parts that the seller had no idea what he had his hands on.....;)

I'll post a video of it on the range later on.

G

Gary,

You have two:clap: I know C310pilot has one on his L4 build. I got a SA for use on my MK II so I could use 7.62 x51 ammo. Nowhere near a real L4 conversion.

I keep an eye out for reasonably priced .303 & 7.62 x51 non corrosive and boxer primed for reloading. That 7.62 x 54 r is really cheap but I hate having to clean the barrel & gas system every time I use it.

Joe

Quote:

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Originally Posted by Joe H

Djandj,

This, I know is extremely frustrating to you. As Peter mentioned earlier,if a group familiar with the Bren could get together and actually handle your rifle I think the problem could be found. You are admittedly not a gunsmith and probably not at all familiar, at least until now, with the workings of the Bren gun.

Over on the Weapons Guild (you may want to inquire over there as most of the participants are semi builders and some may have had the same issues) many of the builders have used the 54R conversion successfully and ones who posted about problems could trace them back to some sort of head-spacing issue. Csmarcher indicated that he had run a HA .308 Bren flawlessly. The barrels, I'm almost certain, HA provided were SA 7.62 x 51, not L4 barrels which are pretty much unavailable in the US. The SA barrels have the same notch as the .303 British. I have a SA 7.62 x 51 barrel and a .303 barrel converted to 8 mm Mauser. I did the same analysis that I previously posted for these two calibers by splitting the heads to be sure the solid end of the case extended past the notch for the extractor, which they did.

In addition to Peter's suggestion maybe try not using the Mag and see if any problems arise. To check to be certain your rifle can only fire with the carrier in the proper position, take a primed cartridge with the bullet and powder removed and place it in the chamber. Drop the bolt on it. Slowly withdraw the carrier/bolt until the carrier is on the verge of unlocking the bolt. Now ease the bolt toward open and try to hold the carrier in the rear position, just about to unlock, Position B in my previous illustration. Pull the trigger. If it fires the primer something may be preventing the carrier from fully locking the bolt. If it doesn't fire try again with the carrier half way to locked position. You may have to remove the return spring for the test. Of course the striker spring has to stay in place. If I had your gun I'd check headspace first then do this test. If it headspaces ok and fails this test I'd be trying to find out why carrier is not returning consistently to fully locked position.

IMO either the headspace is too loose for the 54R or for whatever reason it is intermittently able to fire out of battery or at least not fully locked up. Drag on the return cycle, possibly a mag issue. Other than that I'm out of suggestions :confused:

Joe

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Great Idea Joe. I just got my feeler gauges in today and will get you a headspacing measurement. Then I will follow your directions and see if I can figure out if it can be fired out of battery. I have no idea how to shoot the Bren w/o the mag as it's not very easy to just drop a case in from above. Even it I could, having only one round in 60 going boom could take a LONG time. BTW as we all know, I am NOT a gunsmith and I am not adverse to sending the whole rifle (with plenty of my Russian ammo) off to anyone who thinks they can trouble shoot it. I am willing to compensate them for their efforts. I did this with the builder. I sent him 80 rounds of the Russian steel cased so he could tailor the gun to shoot THAT ammo. He may have been able to shoot all 80 rounds without difficulty (or maybe he didn't shoot all the ammo - IDK)

I will measure tonight and report back. Thanks again to all of you guys and your help and suggestions!

OK gang - here are the new findings.

1. Headspacing. Once the bolt slides down into the locking shoulders, there is no perceptible movement forward or back wards. I was unable to even get the .001 feeler gauge between the bolt and the shoulders. (assuming from Joe's pic posted above, that the measure of the headspacing is the movement of the bolt forward and back once down in the shoulders - if not tell me what I am looking for

I have attached more pics of the components just in case.

2. Firing out of battery. Per Joe's recommendation, I tried pulling back on the charging handle incrementally until it would at what point the firing pin would discharge the primer. the results per the video = it does appear that it will fire with the bolt slightly out of battery (I think that is what the video shows)

https://www.milsurps.com/images/impo...sovogspu-1.jpg
https://www.milsurps.com/images/impo...ugnxloin-1.jpg
https://www.milsurps.com/images/impo...k4nzfxch-1.jpg

Charging handle in it's full forward position.
https://www.milsurps.com/images/impo...uc05wydc-1.jpg
Charging Handle pulled back to the point where it would still fire the primer
https://www.milsurps.com/images/impo...dm0ruyf6-1.jpg
https://www.milsurps.com/images/impo...zbpqmdof-1.jpg

A VIDEO BELOW showing from the bottom of the receiver the point at which it would still discharge the primer.
http://vid1200.photobucket.com/album...psfp8fne2r.mp4

Now I can't explain how if I pull the charging handle back all the way and it falls with full power how the bolt can wind up being slightly out of batter when it fires.

What do you guys think?

If the head space is too tight, then yes. You will get a breech explosion. If excessive, then you will get a separated case, or even worse. A Blow out / Breech Explosion!
The H/S limits are: 0.64"- 0.74". I looked at your photo's & say. you need to open your headspace from. 0.01" Thou. This is FAR Too Tight!!!.....Because yours is a semi-auto conversion & striker fired, I assume? The inertia of the piston extention going forward & even hitting the head of the striker. Albeit SLIGHTLY diminished from a 'Normal' blow.
May well cause the striker to fly forward & hit the case primer. It would SEEM to Me from looking at your photo's. That your headspacing is In sufficient!...

When the breech block is fully locked and safe - that is fully raised and positively locked in front of the locking shoulder - the cocking handle will still have .5" to go until it reaches its most forward point.

This is another mechanical safety

This is due to the fact that the locking ramp at the rear of the piston extension has ALREADY lifted the breech block up into its LOCKED position. THEN the locking ramp must move a further .6" forwards before the cocking handle has reached the end of its possible travel.

Sorry to disagree with (or misunderstand) some of the threads above but looking at the pictures of the semi autos (and certainly on out standard auto's) and the movie clip, the guns cannot fire in an ulocked state while the locking bent at the top of the breech block is engaged with the locking shoulder.

Off the subject a bit but to emphasise the action of the locking ramp on the piston extension. It is this ramp that acts on the rear of the breech block during the forward action. In doing so, the locking ramp is trying its hardest to lift the rear of the breech block which as a result frictions very hard against the roof of the gun body as it runs forwards. In fact it causes a measurable degree of friction that in normal circumstances you would want to eliminate. But on the Bren, this friction is a godsend because it is very effective at slowing the action of the gun right down. We come to a sensible compromise in the Bren by ensuring that the friction surface is restricted to two 'runners', one at each side of the top of the gun body (have a look......, that's the reason!) and that's why we put a smear of oil on them while preparing the guns for action.

This friction laden movement is measurable in time too because using timed high speed video students can see and time the NON-friction loaded rearwards action with the friction loaded forwards action. (Not scientific I agree and there's more to it than that but illustrative of what us students needed to see!) Not a lot of people know that!

Thank you Peter I think I came to the same conclusion last night. If I am correct, the bolt should have a slight bit of travel back and forth even when locked down into the shoulders right? ( how much exactly, still not sure as I've seen posted above anywhere from .03 to .05 by Joe and now .64 to .74 by you) But, in any event, as my headspace is effectively ZERO, the bolt does not move AT ALL when locked into the shoulders. I thought that one possible cause is in fact the ammo in that if a round's rim thickness for example varies even .002 from the "norm" of .063, then the bolt will not lock down into my shoulders - or maybe not lock down all the way. This would mean that the rifle may possibly be firing without the bolt being locked down all the way. Wouldn't that cause the bolt to open too fast? Allowing over pressured gas to burst the cartridge and then flood the receiver up to the mag and blow it up?

So gang... tell me the proper headspacing for this thing? I've heard .03 all the way up to .74.
Next - correct me if I'm wrong, but the easiest way to adjust that headspacing would be to take out my locking shoulders and gently file it down thus making the headspacing gap, right????

I will await the group consensus. And again can't thank you all enough for the help.

Do heed the experts... but here are a few thoughts until they reply... The locking shoulder is a hardened part... filing away the surface will be a bit challenging (hardened... and retaining the proper uniform angle of the engagement surface) and also potentially leave behind softer material that would be susceptible to being battered (compressed) by future firing pressures. These shoulders were originally manufactured in varying lengths so that one of the proper length was selected when setting up the gun... contact Brian at BRP as I think he has multiple sizes for sale here in the US... you will need to measure yours and let him know what length you need... He is a machinist and gun builder so he'll understand what you're asking for. I would suggest swapping out yours for a shorter version rather than trying to modify the one you have.

The screw holding in the shoulder will have been peened so removing it will be interesting... but I'm sure the experts here can give you the best way to approach this swap out process.

email: info@brpguns.com
phone: 301-807-5234
mail: BRP CORP
188 Pickle Simon Rd.
Winder, GA 30680

Related Question:

BRP also has barrel shims... does the effect of introducing a shim on the barrel engagement surface just tighten up the barrel nut and receiver body interaction... or would it also decrease the depth that the barrel inserts into the receiver body - opening up the headspace? Could putting one or two of these shims on the barrels achieve the desired bolt to barrel gap?

djandj,

From your description your headspace is far too tight (nonexistent) just as Tankhunter posted. I didn't see any shims on the case head so if you add the .003" shim I suggested plus the minimum .002" between the bolt and LS without the shim you should be reading .005" between the bolt and LS. To explain the numbers Tankhunter mentioned and I think he means .064" to .074". The case head is theoretically .063". So if the bolt could only move .001" then the headspace would be .064" far too tight for operation of military firearm. I suggested .063" +.003 +.002= .068" Bolt can move .005" (.068"-.063"). The upper level is .074 - .063=.011 that the bolt can move. The .074 is commonly called a Field gage. If the firearm exceeds this the rifle is removed from service and repaired. You do not use the Field gage to build a new rifle.

Peter's .6" range numbers are referring to the amount of carrier travel after lockup and before the FA Bren fires, I think.

Peter,

Depending on how the striker is set up it is possible for the semi Bren to be fired from I what I'm referring to as an "out battery condition", that is the carrier is not fully forward (but the bolt is locked) and short of the same position it would have to be in for the FA Bren to fire. The firing hammer on FA Bren is the piston post, which is part of the carrier. It physically cannot hit the firing pin unless the carrier is in the correct fully forward position which allows about 1/2' of travel before the bolt unlocks. In the semi the hammer (striker) is totally separate from the carrier and depending on it's configuration it can hit the FP and fire the gun without the carrier being in the same position as it must be in to fire in FA.

Dj,

Wally G is correct about messing with a locking shoulder. BRP is a great outfit to deal with and is the only source of various sizes of locking shoulders. I screwed one up and had to make new one out of steel that could be hardened. I have ground them back very carefully using a disc grinder and a homemade jig to assure the correct angle. A file probably won't work. You need emery paper and a flat surface like a piece of plate glass. .005" is a lot to remove by hand. You must maintain the correct angles. A sketch I made of one is attached. I've used a micro air pencil grinder to remove the peening on the LS. A dremel should work.

Be sure you understand what is being suggested and what you have to do before you do anything to your locking shoulder. Best for you would be as Wally G suggested and get a new one .005" smaller and try it out. You need a dial caliper to measure what you have (overall length) to tell Brian what you need. I don't think the numbers on the LS mean anything. The armorers would just sort through the pile until they found one that worked. I'm sure Peter can comment on that.

I've never used the barrel shims Wally suggested. If you try this make sure the bolt does not end up bearing on the receiver stops before touching the cartridge.

Joe

Thank you Joe and Peter. I absolutely will listen to the experts. So it would appear that I need about .005 worth of HS added. So, as I understand it, it's either get a shorter LS or barrel shims. The ones I see listed at BRP are .002 (Bren Barrel Shim) so a bit tough to make .005 out of those. Do they come in different sizes? I couldn't find them on the schematic at BRP. where do they go? Looks like they are easily reversible and perhaps even easy enough for me to install.

If I understand, it looks like the shim would keep the barrel from going as far back into the rifle as it does now thus created HS. Are there other issues to address if the barrel is shimmed and thus not going in as far as it does now?

Thanks again guys.