54R Bren Issues

[Joe H]

Gary,

You have two 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

[djandj]

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

Joe

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!

[djandj]

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)





Charging handle in it's full forward position.

Charging Handle pulled back to the point where it would still fire the primer



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?

[tankhunter]

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!...

[Peter Laidler]

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!

[djandj]

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.

[WallyG.]

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

[WallyG.]

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?

[Joe H]

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

[djandj]

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.