Ream or New Locking Shoulder

Hello, I'm new to the forum but have been building for awhile now. I guess I've been lucky since I'm building my 4th Semi-Bren and have not had this problem before.
Too tight of a space between the locking shoulder and barrel will not allow the bolt to lock up. Is it easier or more recommended to try a bunch of locking shoulders or just ream and adjust the barrel? I don't know what kind of variation there is in the locking shoulders in order to give me enough clearance. Trial and error I guess.
Any advice from those that have had the problem would be welcome.
Thanks, Steve

Easiest starting point will be adusting the gap with a shorter locking shoulder... a source for a large range of sizes in the US is: 30: Bren Locking Shoulder - BRP CORP Store

Thanks WallyG. Ordered them today. Now to get that pesky screw loose.

You are describing insufficient CHS. If I'd answered first I'd have asked you a few Q's to start with. For example. WHEN does the breech block fail to lock up? Is it when you are using the the .064" GO gauge? Then I'd ask, by how MUCH does it fail to lock up? What happens when you try a different barrel? Does a different barrel make it tighter or looser.

Answer those and I'll tell you the rest.

If this is a reweld, are all the dims correct?

Then there's the breech block stops and running clearances and all sorts of things that are associated with it.

Maybe Tankie and Skippy could come in here too. They're Bren era Armourers too...........

when I got a spare barrel for mine the HS was too tight
because I was set up with 1 barrel I made the second barrel fit by reaming and shortening the breach end so the bolt would close

I'm no expert and I have not stayed at a Hotel lately... My reply presumed that this was a US reweld and a large pool of barrels/bolts to try was not an option. By default the other adjustment point that can be changed out is the locking shoulder... and at a relatively reasonable expense. This is a crude adjustment but might be appropriate for a receiver that has been cut and rewelded at multiple points affecting this critical interplay of the components. The rest of the geometry issues and a proper set-up proceedure are best left to the pro's like Peter, Tankie and Skippy.

It fails to lock up with or without a .064 gauge. It is my 4th reweld but the only one with a problem. Heat shrinkage finally got me.
It's difficult to get a measurement that makes since, but here's what I get.
With a .064 Go gauge in place I get 4.355" from the face of the gauge to the locking shoulder. The area I measured to on the locking shoulder was just where it breaks over the edge. Hope you can visualize what I mean.
I have two barrels that fit and both give the same dimensions(within a .001).

On one of my Semi's I had a similar problem but by milling a few thousands off the bolt, where it mates to the locking shoulder, I was able to get proper lock up and it shoots really nice. Didn't want to do that this time since I fear I need more than a few thousands and I don't want to mill thru the case hardening.

Thanks for all the suggestions so far.

It just sounds to me like locking shoulders won't fix your problem because the variation between the selection is insufficient to rectify the shrinkage you have. I don't think that the shoulders are case hardened. They are simply tough material and I'd start by surface grinding, say, .010" at a time off the angled locking surface until the breech block JUST closes over the .064" gauge. That way, you have retained the working geometry of the breech block in relation to the breech, piston post and therefore mechanical safety and so on and on. Not that I have ever welded one up again. But cut a few up! and repaired about a zillion of 'em

Thanks Peter,
Prior to your post I decided to try and mill the backside of the locking shoulder to preserve any hardening of contact surfaces.
Success! I now lock up on a .064 gauge and do not on a .067 gauge. I now have to slightly elongate the srew hole in the receiver and stake everything in place.
Thanks tremendously for your thoughts.

Yep......., on second thoughts I think that your idea is the right one because a) elongating the locking shoulder screw hole is slightly academic as it is a re-weld in any case and b, it leaves the remainder of the geometry as it should be. But I would advise that the screw is just a means of holding the shoulder in place and does absorb the recoil. The actual RECOIL energy or force is directed through the locking shoulder rearwards and back into the body of the gun. For this reason I would try to make sure that the rear surface of the re-ground locking shoulder matches/mates up with the surface area of the body supporting the rear of it as best you can get it

Please ignore all thoughts of a .067" gauge. This size does not feature in any Bren EMER. The No-Go is .074"

Right............ First detail on the firing point. Down test and adjust. With a magazine of 30 round, ........LOAD............! READY..........! Ooooops, Sorry..., just got a bit carried away and dreamed that I was about to run the Bren ranges again!

Peter, as you said I got a real good fit to the body with the locking shoulder and still have some slop in the screw hole.

Just put a full magazine (well 28 rounds) thru it and it ran really sweet.

Now to clean it up and Dura-coat it.

Again thanks to all.

Thought I would post a picture of a few of my Brens :)

Havent dropped in for a while & only just seen this!

Peter pretty well had it covered! The only 'usual' gauge sizes for 'Normal' use (Usually at Unit level) would be the same for the Enfield Rifle. .064" -.074", that gives you eight thou to SAFELY play within!

As Peter points out. There are many variables in your area of construction. As it's a reweld, there will be MUCHO metal missing inistially!...getting it all back together again, within the correct tollarance sizes. Will be a tricky & time consuming project! so much to deal with here at a cut-up level, you have done well to get it all back & the internals running in line & correctly in the first instance!

I know that Peter & myself, had absolutely NO trouble back in the day. CUTTING Brens up to destroy them!...........Makes me weep to think about it now. But, back then, there were thousands of 'em floating about in the system. & you couldnt store THAT many in War reserve!....

It's hard enough these days Deactivating good running examples. Without the thoughts of them being Gas-Axed up for parts kits!.....:(

Just to REALLY pile on the misery. The Aussie Govenment, is cutting up all it's 7.62mm Converted L4's!.....Now that REALLY upsets ME!.....:mad: