Bren Mk 2 Recoil Spring Issues

djandj,

My experience with the semi striker Bren is that you will have to operate at the 3 or 4 gas setting with the proper springs whether using .303 British or 7.62x54R. The original FA Bren operated at the #2 setting. The semi has additional recoiling parts (the striker) and an additional spring to compress so it requires more gas.

Definitely use both springs. They are designed to work as one.

It would be interesting to see how yours and Wally's return striker spring is set up. At 3/4" OD and on the return rod, unless something is altered, it cannot go back into the stock with the return rod so it must compress as the bolt moves rearward. My striker spring is .35" OD and moves with the return rod into the stock. It compresses as the bolt moves forward.

Below is a typical set up (not mine), striker spring shown, return spring in buttstock:



Attachment 53330


Joe

New recoil springs will help... one of the design features of Len's semi conversion is the removal of the buffer... which would explain the violent recoil impacts against the rear of the lower slide... presuming that your recoil springs are weak or missing. I believe he did this to make more room for the striker to reciprocate. Adding a plug in the base of the return spring tube would add more "spring resistance to recoil." I have never had to do this but I've not put large volumes through my Brens. Another item might be that the barrel gas port has been opened up to much and is venting more gas than needed despite your low setting... another Len feature is that he has been known to drill out oversized the small hole in the gas regulator... so you might be using more gas than you would expect... you could obtain for little cost an additional gas regulator and determine if yours has been so altered or not. More gas was needed on some guns to overcome the resistance of the striker and the striker spring. I'm not proficient at posting pictures... if someone wants to... I can provide images of Len's design features for posting.

Joe:

Same geometry as in your picture... but the larger diameter spring has a larger socket cut into the striker to hold that end... and there is no buffer plate so the other end of the spring seats against the rear surfaces of the lower slide. All kept in place by the recoil rod. The striker spring does not enter into the stock and is compressed by the striker during recoil. I'm still thinking that either the barrel gas port or the gas regulator might have oversized holes and are contributing excess gas to this scenario too. If the gun has lost its recoil springs in the stock tube... I agree... the striker spring alone would fail rather quickly.

Quote:

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Originally Posted by Joe H

djandj,

My experience with the semi striker Bren is that you will have to operate at the 3 or 4 gas setting with the proper springs whether using .303 British or 7.62x54R. The original FA Bren operated at the #2 setting. The semi has additional recoiling parts (the striker) and an additional spring to compress so it requires more gas.

Definitely use both springs. They are designed to work as one.

It would be interesting to see how yours and Wally's return striker spring is set up. At 3/4" OD and on the return rod, unless something is altered, it cannot go back into the stock with the return rod so it must compress as the bolt moves rearward. My striker spring is .35" OD and moves with the return rod into the stock. It compresses as the bolt moves forward.

Below is a typical set up (not mine), striker spring shown, return spring in buttstock:



Attachment 53330


Joe

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Yep - my setup looks similar, but I don't have any spring in the butt stock - just one (larger 3/4 inch) spring. Len got back with me and is sending more springs(s) - I will report back. I also ordered the original MK II replacement springs so I may try them as well.

Thanks,

David

While I don't know anything about these single shot variants, I have to say that the 'hammer spring' shown in thread 11 looks totally inadequate, not man enough for reliability and doomed to failure. That's only my opinion based on absolutely nothing more than a deep mechanical understanding and many many years experience with Bren guns

Quote:

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Originally Posted by Peter Laidler

While I don't know anything about these single shot variants, I have to say that the 'hammer spring' shown in thread 11 looks totally inadequate, not man enough for reliability and doomed to failure. That's only my opinion based on absolutely nothing more than a deep mechanical understanding and many many years experience with Bren guns

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Peter,

In the world of fully automatic Bren guns it would appear you are correct. Actually the semi-auto Bren works quite well with this setup. It is not obvious from the picture but in operation as the bolt moves rearward the spring does not compress but moves rearward into the butt-stock with the return rod. As the bolt and return rod move forward the striker spring is compressed since the striker is caught on the sear. The spring you see is not compressed by recoiling parts but by the return spring rod on its forward motion.

I doubt the semi version would ever be as reliable as the original FA Bren. Unless the semi's have the gas system modified there is no "reserve". I've drilled out a regulator and barrel to make the gas flow at #2 equivalent to the original #4 but due to knee surgeries I haven't got a chance to check it out yet.

Joe

Quote:

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Originally Posted by WallyG.

Adding a plug in the base of the return spring tube would add more "spring resistance to recoil." I have never had to do this but I've not put large volumes through my Brens.

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Wally,

The plug doesn't really add additional resistance it just gives the same resistance as the full stroke FA Bren. The striker prevents the recoiling parts from reaching the rear buffer by the length of the striker so that the return spring is not compressed to its design compressed length. It is short by the length of the striker. The plug allows full return spring compression at the shorter semi stroke. It is particularly important in the design I used since the striker spring is compressed on the return.

Joe

Joe:

Thanks for the logic behind the plug... makes perfect sense. I'm thinking that djandj's problem is that someone removed the recoil springs from his butt and the poor striker spring is not up for the task of running the bolt and bolt carrier back into battery after being crushed by these same parts in recoil . Lens design uses the original recoil springs that are behind the return spring rod to cycle the gun. The large striker spring is only intended to drive the striker forward to fire... and being a spring... also absorb some of the recoil forces from the bolt group and striker.

Quote:

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Originally Posted by WallyG.

Joe:

Thanks for the logic behind the plug... makes perfect sense. I'm thinking that djandj's problem is that someone removed the recoil springs from his butt and the poor striker spring is not up for the task of running the bolt and bolt carrier back into battery after being crushed by these same parts in recoil . Lens design uses the original recoil springs that are behind the return spring rod to cycle the gun. The large striker spring is only intended to drive the striker forward to fire... and being a spring... also absorb some of the recoil forces from the bolt group and striker.

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Now see THAT may make some sense. I will check when I get home to see if there is a spring in the stock or not. But it sure does seem like my striker spring is eating all the impact as it stands now.

djandj,

Wow! possibly firing the Bren without a return spring. The way mine is configured the bolt would not return, but with the striker spring compressing on recoil as yours is built the striker spring could be doing the work of the return spring. It seems hard to believe that it was put together without the return spring but possible since a trial hand cycle may not reveal the problem.

Joe