54R Bren Issues

[Joe H]

I don't have any semi-auto Bren guns here. My two guns are both restricted, post sample originals. There may be some to look at in PA. Wiselite Arms was there last time, (set up directly behind me in fact), which would be nice because they did a much better job than Historical Arms IMHO. They had them in 7.62x54R too if memory serves. I don't know if they're still building them or not since that was five years ago.

Brian,
Where in Pa? I'm in Western Pa near Pittsburgh.
Joe

[CINDERS]

All help/ideas are welcomed

I only that I had the pleasure of firing one once but just as a novice can it be a timing issue that the case has started to move with the breech assembly whilst the projectile is still in the barrel and not clear of the gas port which will obviously relieve the internal pressure. You would not notice this until the case ruptured, then again 60 rounds prior to that no incident, so is it the ammo given the copious quantities Russia produces (Lot No. ?) there is a Bren barrel brand new for sale on usedguns.com.au but it is very expensive and you probably would not get it out of this country...just trying to assist with some obtuse thinking

Postscript ~I got to thinking about the timing and the rupture and copied the Pic from page one and it looks like a drag mark from a rim on the cartridge soooo my theory is that if it happens on the first stripped round under the tension of 20-24 rounds behind it then it may slow the carrier down just that tad. Now going on what has been said that some of the semi auto versions may not have a a built in safety device to stop a slam fire could the striker drop and fire the round before it is all locked in the chamber. The timing gap you would not notice before it all went bang and the mag flew off.... what say others ?

Joe H stated about semi auto Bren's

The upper tab is many times flush with the front of the striker allowing the rifle to be fired if the carrier is short of the correct "in battery" position. If the tab is located 3/8" behind the front of the lower part of the striker then if the carrier is not fully forward the lower striker will hit the carrier and not fire. I don't know if this safety feature is built into djandj's bren. Most of the semi's I have seen do not have this feature.

[Vincent]

What happens if you only load 29 rounds instead of 30 in each magazine?

Here’s why I am asking. Every time the bolt moves back it lifts all the rounds in the magazine.

With these closed bolt setups and a full magazine the bolt is lifting all 30 rounds when it’s pulled back to load the first round.

Is it possible that there is not enough room in the magazine for the rounds to be lifted when it’s full and the first round is being damaged by the bolt as it is pulled back?

You could eject the first round from a full magazine and inspect it.

[Brit plumber]

On a semi, what stops the firer releasing the striker onto an unlocked breech? Obviously on a normal Bren this could never happen but a semi? Thinking along the same lines as Vincent above, the extra drag of a full mag may be slowing the carrier down and it doesn't lock up correctly.

[Joe H]

OK Guys. Feeler gauges ordered. I will try to get an accurate measure of the headspacing so we can start there. After that, it has been hypothesized by Troy at Barrel Works that since the gun tends to go BOOM on the first round of the mag each time that it could not be fully locked up when it fires. (IDK) He had suggested looking at the extractor and making sure that it wasn't getting in the way of a solid lock up. Who knows? But head spacing measure first. I will then report back.

djandj,

Magazine issues???

The first link I referred djandj to and I posted previously above had this reply that I posted on The Weapons Guild Forum in 2012. It was about the same problem of 7.62 cases rupturing at the base.

QUOTE "From my experience the mag was overloaded. Other guys may find it different but until I got my ZB 39 mags altered they were popping out and jamming. It sounds like the round was jammed and went off before the bolt was locked or it would be my first guess the the overloaded mag and consequent drag on the bolt prevented the carrier from going fully forward and just barely locking but not fully forward so that the pressure was not low enough for the bolt to open causing the split. On the Bren the carrier has to move about a 1/2" before the bolt unlocks to allow the bullet to clear the barrel and the pressure to drop.

Did you modify the striker so that it couldn't fire unless the carrier was fully forward?" QUOTE

There is plenty of space in the ZB39 mag, which I assume you are using, for the bolt to push the rounds up into the mag as the bolt is pulled back. The ZB39 mag with a capacity of 25 rds was designed for the 8x56R, a rimmed round similar to the 7.62x54r. You can only get 15 to 20 rds max of 7.62x54R into an unmodified ZB39 mag. At 20 rds its not the spring tension that limits the capacity its the fact that the curvature of the ZB mag does not fit the 7.62 rd. The geometry of the two cases is different. As you get close to 7.62 capacity (15-20rds) the tips of the cartridges start to dip into the mag eventually stopping on the forward lip of the mag. This is what limits the capacity of the ZB-39 mag using the 7.62x54R. I've found using 7.62 x 54R dummy rounds that as you get close to "capacity" the tip of the bullet starts to hit the forward lip of the mag. This steals energy from the closing bolt possibly causing the carrier not to close in the full forward position. The rounds would cycle but I could see the damage to the tip of the bullet hitting the forward lip of the magazine as it cycled into the chamber.

Brit is exactly correct in that the carrier of a FA Bren must be in the full forward position "in battery" for the gun to fire. In the pic below an open bolt FA cannot fire unless the rear of the carrier is in Position A in the pic below. The piston post which fires the round and is attached to the carrier cannot contact the firing pin until the carrier reaches Position A.
In the striker- fired semi Bren if for whatever reason, mag drag etc., the rear of the carrier only reaches Position B and the striker tab is flush with the face of the lower part of the striker (typical of many striker fired semi Brens) then gun will fire with the rear of the carrier in Postion B probably allowing the bolt to open too soon with pressure on the cartridge causing the problems djandj is experiencing.

Prior to my 2012 reply (above) I realized the typical striker fired semi could fire out of battery. I redesigned my strikers with an offset between the tab and the face of the lower section so if the carrier was in Position B the lower part of the striker would hit the carrier and the tab would not contact the firing pin.

Joe

[Joe H]

All,

Below are pics of how I altered the semi striker so that the rifle could not be fired "out of battery". These are pics of my rough prototypes to show how it works. The second pic shows the set up at the instant of firing. The length of the firing pin and tab offset have to be coordinated so that tab cannot hit the FP unless the carrier is in the full forward position. About 1/4" must be left clear to the rear of the tab so that the recoil buffer will work.

Joe

[Joe H]

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 ----------



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

Djandj,

I re-read this thread from the beginning. I found the quote above. There is no way 25 rds of 7.62x54R will feed correctly through an unmodified ZB39 mag in a Bren. Yes you can stuff them in an unmodified mag but they will not free freely into the chamber. In my experience 20 rds is the ultimate limit unless the magazine has been modified which takes some doing for 25 rds of 7.62 x 54R.

Try 10 -15rds in the mag and very possibly your problem will go away if the rifle is head-spaced properly. You should also check out the striker "out of battery" issue.

Joe

[Brian Dick]

Harrisburg, PA.

[Peter Laidler]

That is an ingenious way of ensuring that the gun cannot fire unless the breech is fuloly closed Joe. Is that your invention or the standard semi-auto norm? The hammer part of your hammer block is acting the same way as the hammer part or what we call the 'hammer face' of the piston post in a standard gun. The piston post and your hammer cannot hit the striker with sufficient force unless the breech block is fully closed/locked. It gets better too because even if the breech block isn't fully closed in your method (or the standard piston post method0 and you decide to close it manually somehow, it still won't fire due to insufficient energy remaining within the hammer to initiate the primer.

I know it's a bit anorakish but keep thinking to myself that if we could get 6 or so UK and US/Can et al Bren forumers together in a classroom together with a few scrap Brens, paper pencils and a black-board we could solve this problem in an afternoon and all go for a beer in the evening. Are you game Tankie and Skippy........, between us we've fixed a zillion of them - and know them inside out!

[Joe H]

Peter,

I started building my first Bren semi in 2008. I bought the striker from one of the "Professional Bren Builders" . The upper tab was flush with the face. I began to get concerned that the design really had no way to prevent out of battery discharge. No one seemed to have any problems nor did I with .303 British and standard .303 Bren mags. As people began to build and convert to 7.62 x 54r a few problems like Djandj's began to appear. Most could easily be traced to loose headspace but a few indicated problems with the carrier not closing properly. I became more concerned and in 2011 reconfigured my strikers as shown above. I posted my ideas on The Weapons Guild Forum. I don't know if anybody used my idea or not or if somebody else had already thought of it and was using it unknown to me. There are more than one design variations around. There is another type of striker design which could be on djandj's Bren (can't tell from his pics) that utilizes a striker spring that is not on the return rod and eliminates the buffer which may have the proper out of battery safeguards. There also is a hammer fired variation. The one I built was the typical design used by most individual builders.

"Professional" Semi Bren building is pretty much a cottage industry here in the States with a number of us individuals building our own. As you are probably aware there never has been any testing done to any real extent on the semi designs. Nothing like the 100,000's of rounds and years of design that went into the original ZB/ Bren design. I for one am totally impressed with the Bren design and I'm happy to a least have working semi-autos.

Joe