54R Bren Issues

[djandj]

OK so now the "explosive update" I got the rifle back from Troy who very kindly agreed to re-ream the barrel for me. I used a DIFFERENT spam can of 54R. (see pic) Fired 60 round FLAWLESSLY (no case fatigue at all) then.... on the first round of a fresh mag. BOOM!!!! The case failed on BOTH sides (see pic) and blew the mag out of the rifle!!!!. The Builder claims it's and "ammo issue" and won't help. (of course he build the damn thing with the express purpose of shooting Russian steel cased surplus ammo....but that's another issue).

So.... gang, I'm on my own with this thing. Need ideas. How does the rifle cycle 60 times perfectly and then have a catastrophic failure like this! Again, seems clear that the cartridge is unsupported in two places where the barrel is beveled in the back so... does head spacing matter when the casing is unsupported on the sides no matter how close the rim of the case sits? Keep in mind that when he first sent the rifle to me the first barrel caused every cartridge to blow out, but for whatever reason, the gas pressure was never enough to blow up the mag. When I got it back, the new barrel (or combination of barrel and rifle) now causes a BOOM ever 60 rounds or so.

At least he seems to have fixed the recoil spring issue. I cycles fine, but does have the LITTLE problem. We need to resolve. Can't expect any casing to withstand the pressure without the support of the barren or other mechanism.

Thanks for the help. I'm on my own and don't build guns myself so....... All help/ideas are welcomed.

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[Joe H]

so... does head spacing matter when the casing is unsupported on the sides no matter how close the rim of the case sits?

Djandj,

I know I can't give you any new advice. In one respect or another your problem is "head-spacing". You comment above indicates you don't understand the problem. Both TactAdv and I told you Troy wasn't going to solve your problem since you only sent him the barrel and consequently he couldn't check for a headspace problem.

IMO it's one of three problems:

1 - Head-spacing is too loose. It may work for .303 but I doubt the 7.62x54R is as tolerant as the British round. The 7.62 only has to move a very small amount for the pressure to see the thin wall od the case.

2- Timing is off so that the bolt is opening too early allowing too much pressure on the case as it extracts.

3-The bolt is hitting the two lugs on the receiver before it closes on the cartridge. Could happen but not as likely as the two above.

Here is some relevant reading material:

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Headspace 101 for .303s in The Lee Enfield Forum Forum

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The Bren can be checked for headspace with practically no tools or gages. More to follow.

Joe

[Joe H]

Djandj,

Here is a simple way to check headspace on a Bren. The rim thickness on the 7.62 is .063" so you can use the same headspace dimensions as the .303. The Bren was never designed for the 7.62x54r so I'd keep the headspace as low as possible.

Strip the frame, carrier and bolt. Remove the firing pin and extractor from the bolt. Take a properly resized MT case or unfired 7.62x54r case with the powder and bullet removed. The 7.62 x 54r is within .001" of the .303 british rim so you can check using the .303 headspace dimensions. Check the rim thickness. It should be about .063". It is a little difficult to check since the head is not flat. Glue on a .003- .004" piece of shim stock on the head of the case. Slide the case in the barrel. Now only install the bolt without extractor, no carrier spings etc, only the Bolt. Push it into the locked position. Push the bolt forward with your finger. The case should be snug under the bolt. If it isn't check Item 3 above. With your finger still pushing on the bolt and using a feeler gage you should have between .002" and .005" between the bolt and locking shoulder. If its .010" or better you may have problems. If its .015" plus IMO you definitely will have a problem. You probably will have to replace the locking shoulder with a longer one.

Every time the bolt closes the relationship of the carrier and bolt should be as in the attached pic. The carrier should have to travel 3/8" to 1/2" before the bolt unlocks. If you don't you may have problem 2 above.

The second pic shows the gap between the bolt and locking shoulder on a Bren that was having the same problems as you.

Joe

[Joe H]

Djandj,

Here is a simple way to check headspace on a Bren. The rim thickness on the 7.62 is .063" so you can use the same headspace dimensions as the .303. The Bren was never designed for the 7.62x54r so I'd keep the headspace as low as possible.

Strip the frame, carrier and bolt. Remove the firing pin and extractor from the bolt. Take a properly resized MT case or unfired 7.62x54r case with the powder and bullet removed. The 7.62 x 54r is within .001" of the .303 british rim so you can check using the .303 headspace dimensions. Check the rim thickness. It should be about .063". It is a little difficult to check since the head is not flat. Glue on a .003- .004" piece of shim stock on the head of the case. Slide the case in the barrel. Now only install the bolt without extractor, no carrier spings etc, only the Bolt. Push it into the locked position. Push the bolt forward with your finger. The case should be snug under the bolt. If it isn't check Item 3 above. With your finger still pushing on the bolt and using a feeler gage you should have between .002" and .005" between the bolt and locking shoulder. If its .010" or better you may have problems. If its .015" plus IMO you definitely will have a problem. You probably will have to replace the locking shoulder with a longer one.

Every time the bolt closes the relationship of the carrier and bolt should be as in the attached pic. The carrier should have to travel 3/8" to 1/2" before the bolt unlocks. If you don't you may have problem 2 above.

The second pic shows the gap between the bolt and locking shoulder on a Bren that was having the same problems as you.

Joe

3-The bolt is hitting the two lugs on the receiver before it closes on the cartridge. Could happen but not as likely as the two above.

Djandj,

Is this what is happening???? Use the feeler gages and determine what the amount of space is between the rear of the case and the face of the bolt which is stopped on the receiver lugs? Quote from above " If its .010" or better you may have problems. If its .015" plus IMO you definitely will have a problem." The bolt should bear on the cartridge case. The receiver lugs (stops ) are there to prevent the bolt from battering the barrel.

If your assessment is correct and the bolt is stopping on the receiver lugs before contacting the case just as Mr. E posted the gun cannot be properly head-spaced. In the current configuration the operational clearance which should be .002" + is zero.





Joe

[djandj]

Djandj,

Is this what is happening???? Use the feeler gages and determine what the amount of space is between the rear of the case and the face of the bolt which is stopped on the receiver lugs? Quote from above " If its .010" or better you may have problems. If its .015" plus IMO you definitely will have a problem." The bolt should bear on the cartridge case. The receiver lugs (stops ) are there to prevent the bolt from battering the barrel.

If your assessment is correct and the bolt is stopping on the receiver lugs before contacting the case just as Mr. E posted the gun cannot be properly head-spaced. In the current configuration the operational clearance which should be .002" + is zero.

Joe

Thanks Joe. As you can hopefully see in the pics, everything is lined up for an exact fit. There is NO space between the bolt and the stops (except along the upper part looks like I can get the .002 gauge in a little way - but then it stops further in) and No space between the cart. and the bolt. As near as I can figure it, the pocket formed is exactly the size of the round. (unless of course the round is out of spec...) Once locked in the shoulders, there is NO movement possible forward or back by the bolt.

[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.