54R Bren Issues

[ActionYobbo]

Don't do anything yet DJ as I have an answer but it's long winded so will come in early tomorrow morning!

was this what you were refering to?

The pics were interesting for me, a total amateur when it comes to the US semi auto rebuilds. I can see now where on the US Semi's, with an extended striker you could fire the gun with the breech block forward but not quite locked.

But back to page 6(?) and locking shoulders. I have a feeling that the locking shoulders are not case hardened but are a hard tough material right through and on that basis you could dafely grind one a tad to suit. I say this as I have just put one to a grinder in a dark workshop and even well into the steel, the grinding colour hasn't changed. Yep....., I know it's not quite scientific or a lab test but to the experienced, it's a good rule of thumb.
If anyone does have a stack of locking shoulders, I'll say once again to ignore the size on them (if there is one!!!!!) and trust in the DTI. To measure them we had a small jig that you could mount a DTI onto. Then you slip the locking shoulder in LOCKING/BREECH BLOCK EDGE DOWNWARDS onto the surface of the jig and the bottom totally flat surface of the shoulder square-up against the rear edge. Hold there with finger and slide the DTI plunger across the flat REAR surface. This is the only way to get a correct reading of the actual length

went and measured my spares
786
803
822

[djandj]

was this what you were refering to?



went and measured my spares
786
803
822

Thanks Mr. E. Nothing close enough. Appreciate you looking for me.

---------- Post added at 09:27 PM ---------- Previous post was at 09:22 PM ----------

Don't do anything yet DJ as I have an answer but it's long winded so will come in early tomorrow morning!

No worries Peter. No luck in finding the right size anyway (at least as of yet)

Thanks,

[csmarcher]

Try going out and buying 100 rounds of GOOD QUALITY 7.62x54R with brass cases and try firing it. I'd bet you don't have the problems that you're having with the crappy steel cased rubbish. I believe Privi Partizan makes it.....

[Peter Laidler]

That was it MrE. I knew I'd written it up somewhere.

Once again the CSM says what others might be thinking - that this ain't a CHS problem but an ammo problem. But being an Armourer I would blame the ammo instead of the gun of course. Great car number plate CSM!

I think that you can carefully stone the locking shoulders that you have - or the rear locking bent of the breech block. You just need a .003 or so running clearance. But please try. Different i8n an Armourers shop as we had a big tray of locking shoulders. But as I said above (thread 131) we didn't box them by SIZE but by largest through to smallest! I certainly have stoned the rear locking bent of an L4 breech block in order that I could compromise in the fitting of two perfect barrels where no barrel washers were allowed.

[Joe H]

I think that you can carefully stone the locking shoulders that you have - or the rear locking bent of the breech block. You just need a .003 or so running clearance. But please try.

I know some have concerns regarding the quality of the commie ammo. I also know the people posting on another Forum consisting mainly of semi builders have used the ammo in their semi-Brens without the problems djandj has experienced. There have been instances similar to djandj's and all have been tracked back to headspace problems.

As Peter noted above let Djandj get his Bren set up properly then if he still has the problem then maybe we can point our finger at the ammo.

C130Pilot's friend Joe has a FA Bren converted to 7.62x54r, not surprising considering the cost of ammo. C310 posted a video on this Forum showing the Bren in operation. Initial problems were too much gas and mag feeding. I know both problems were solved. Smaller gas orifice and a mag that worked with 20rds. IMO if you can get a FA to work on 7.62 it ain't the ammo .
Joe

[Vincent]

I was told the Historic Arms Bren uses an unmodified breech block. And there’s no shortage of them here. So… I am wondering if stoning the breech block is an option?

Djandj would have to replace the firing pin, but that’s much easier than replacing the locking shoulder.

[Joe H]

Dandj,

Removing .004-.005" off the LS (or off the back of the bolt) will be a real pain in the a-s to do by hand, but probably the safest way, if you are not comfortable with setting up and using high speed machinery. You will need a perfectly flat surface, I use a piece of plate glass and some emery paper or a good flat stone.

I would do the LS. If you can get access to a disc sander (grinder) it will take just a few minutes. If the table can be rotated, depress it 25 degrees, if not make a ramp out of wood or whatever so that the LS bottom face sits 25 degrees above horizontal. Use the cross cut slide to keep the LS square with the disc and the jig or depressed table to get the correct grinding angle. Before starting be sure the face of the LS is perfectly flat with the disc.

You can refer to the sketch of the LS I previously posted on this thread if you want to check the angles.

Just touch the LS to the wheel, don't push hard, you only want to remove about one thous each time you touch the disc and you don't want to heat up the metal so that it changes color. Constantly check the dimension till you have the correct length. The difference between what you want to grind off the face will be the same as the difference in overall length. The effect of the angle is negligible. I'd shoot for .8175 - .004 = .8135" . You can always grind more off but you can't add any.

Joe

[Peter Laidler]

We used what we called 'three corner stones' to stone down shoulders and the like. Not too difficult and once you get going it doesn't take too long. I have done countless No4 cocking pieces, sears etc etc including L1A1 locking shoulders. Plus the odd Bren too of course.

We also regularly stoned back the breech block face if it contacted the barrel while checking CHS.

I'm not sure that you can use an unmodified .303 breech block because the 762x54R has a slightly larger base rim diameter and won't fit into the cart seating.

[Vincent]

Ah! I forgot about the larger rim.

[TactAdv]

IMHO, it is FAR easier to weld up, or take down, the BOLT locking surface. You'll need a coolant-flow grinder to take it down, but it does work well.

Same thing with moving it up (tightening) the lock-up; You can weld up the rear locking surface and the grind to fit the specific locking block in the gun.

For my original select-fire BREn, I am in the process of making two caliber conversions- one, 8mm using one of the mystery re-bored and chambered original .303 barrels that are floating around out there, and two, a .308/7.62mm NATO conversion using an SA 7.62mm barrel. Both conversions will use standard, original .303 bolts with 7.62mm extractors installed. (Magazines are ZB26/30 mags for the 8mm, and ZB-39 mags for the .308. The ZB26/30 mags require a slight opening up of the rear mag well area.)

Both barrels are fitted to lock up tight and smoothly in the barrel recess in the receiver; at that point, current (-ANY-) "headspace" of the chosen bolts with the installed locking shoulder is irrelevant as each bolt will be hand fit to mate properly with it. The goal is to make each conversion such that all that is required is to field strip the gun, exchange the barrel, bolt, and magazine, leaving the installed locking shoulder and all else in place.

As mentioned above, each bolt will have a small amount of weld built up on the bolt locking surface, then ground down to the final fitment. Thus , each bolt is thus "fully committed" to the specific conversion/receiver combination, but since bolts are cheap and available, I judged this the best course of action.

(I have also a 7.62x54R conversion "mostly" done, as I have previous mentioned, though am currently stalled on the magazine.....I have decided the only rational plan is using a modified DP-28 47rd pan, modifying the underside receiver interface to fit and lock in the BREn receiver. Got most of that done, but will still be awhile to get it fully fitted.)

-TomH