54R Bren Issues

[Vincent]

Well, you could conceivably get any number of problems that would cause the gun to fire OOB, in a form of API. Chamber obstructions, stuck or jammed FP, etc., all could cause enough primer contact to set off the cartridge before full dwell is reached. All manner of other semi-auto gun types exhibit this all the time.

One of the things I never liked in all these "semiauto machine gun" design conversions like the BREn, RPD, DP, etc is the necessarily very long FP's that are employed......lots of room to get stuff in there and cause friction or outright jams and these all have very long pin protrusions to begin with. If the FP tip is not fully retracted as intended.....for any reason.....coming round again it can easily function as a fixed FP, especially if the primer cup thickness is not very....thick, or you are dealing with an old and over sensitized priming composition.

Might not be a "steel versus brass case", argument there at all, might just be a very differing primer sensitivity between the two batches of ammunition, coupled with either a sticking FP, or the reverse situation, a long, heavy FP that is allowed to slam forward under inertia??

-TomH

I understand those issues, but this makes me think it’s not one of them.

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).

It’s happening with the first round, when the cocking handle, slot, etc, limits how far the breach block and carrier can be pulled back. This in turn limits the amount of energy stored by the return spring.
But when a round is fired the breach block and carrier travel back a greater distance and more energy is stored in the return spring. So when the breach block and carrier move forward again they are pushed with more force than cocking can provide to lock the breach block.