54R Bren Issues

[djandj]

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

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

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 ----------

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

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

[djandj]

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

[browningautorifle]

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

[csmarcher]

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

[Bruce_in_Oz]

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!

[Peter Laidler]

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

[Joe H]

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

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

[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.

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

[Joe H]

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.

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

[Peter Laidler]

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