54R Bren Issues

[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...................

[browningautorifle]

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.

[Peter Laidler]

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

[Joe H]

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

[Peter Laidler]

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..........'

[djandj]

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.

---------- Post added at 09:55 AM ---------- Previous post was at 09:50 AM ----------

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...................

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,

[Peter Laidler]

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

[Joe H]

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"]

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

[Vincent]

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

[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