54R Bren Issues

[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