Bren locking shoulder size question

Apologies if this question seems dense. I can't figure out which end of the Bren headspace size scale opens up headspace. I believe numbered sized were 3X, 2X, 1X, 00, 0, 1, 2, 3, 4, 5 , 6. Would a #6 provide the tightest or loosest headspace of the range?

I have a Bren project in the works and need a different smaller size locking shoulder to open up headspace a bit. I can't quite make out the number on my current one but it measures 0.815" from the back to the front angle of the wedge. Is there an armour's manual that calls out dimensions of the different sizes? Would like to avoid grinding locking shoulders if possible.

Many thanks in advance,

To be really honest Lima, you are asking the same question that Armourers have been asking since pontius was a pilot! The truth is that while there was a theoretical dimensional sequence, it really bore no relation to numbering as we know it on this planet.

This is what we all had in our workshops and I'm sure Tankie, Son and Skippy will (hopefully) agree with. We had a large partitioned tray and the locking shoulders were placed into the relevant partition based entirely on their measured LENGTH and NOT on the size indicated on the underside.

I suggest that you get a selection of locking shoulders, forget the number thereon and select the one that gives the correct CHS of between .064" and .074". You won't need to have one ground as they are fairly easy to stone given a bit of care - or better still, and don't tell anyone I told you, but just stone the rear of the breech block locking bent to suit

Quote:

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Originally Posted by Peter Laidler

I suggest that you get a selection of locking shoulders, forget the number thereon and select the one that gives the correct CHS of between .064" and .074". You won't need to have one ground as they are fairly easy to stone given a bit of care - or better still, and don't tell anyone I told you, but just stone the rear of the breech block locking bent to suit

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lima,

In the US building a semi auto Bren from a de-mill is fairly common. Once welded up it is typical to have to deal with the locking shoulder to set the headspace on the rebuilt receiver. It is not unusual to have to grind back the locking shoulder to compensate for weld shrinkage. Depending on the amount to take off it can be done with a stone. I've also ground them very carefully with a jig on a disc grinder removing only a small amount at a time and keeping the work cool.

Attached is a sketch of the locking shoulder. I had to make one once. Their availability is limited here in the Colonies.

Joe


Attachment 58398

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Originally Posted by Peter Laidler

...... or better still, and don't tell anyone I told you, but just stone the rear of the breech block locking bent to suit

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:thup: Thanks for the sage advice, Peter. I have a feeling I will be following it. Getting the weld shrinkage to work out within a few hundred thou is almost impossible.

I have gathered up parts for a Bren build and been reading the build threads on the net. I would really like to read your Bren book before I start it. Any update on when it will be published? Also wondering why the publisher hasn't done another printing of The Guns of Dagenham. I have written to them a couple of times now and not received a reply.

Peter - Thank you for the sage advice. So it sounds like there are no hard and fast rules as to the relative size between a 3X and a size 6...

Joe H - I want to fully finish my weld cosmetic finish work in the middle section before making a jig to grind back the locking shoulder. As it sits now, bolt half locks on empty chamber and barely starts to lock up a with dummy round. Better to tight than too loose at this stage.

Vincent - Sent you a PM with a vendor listing the wonderful and engaging Guns of Dagenham book for a reasonable price if you are still looking

The Bren book.......... Good question Vince and everyone else who mentions it occasionally. Indeed, I often ask it myself! The whyole lot went over to Dan Shea at Small Arms Review (SAR)who said that Moose Lake Publishing would publish it under the direction of Editor Rob Segal. Robert moved aside for personal reasons and at that, the Bren book took a loooooong vacation. Out of sight, out of mind so to speak. Family/domestic situation intervened at SAR so.......... anyway. A couple of years ago Frank Iannamico took over the editorship of the book and we spoke several times at Warminster during visits. Alas, the original manuscript and rare archive photos were missing. They were finally found 12/18 months ago but as so many many many times in the past........., nothing. So I'm not holding my breath.

Maybe a few chase-ups to Frank or Dan at SAR or Moose Lake Publishing might bring forth something

This may sound Peter but as you wrote the book, do you retain the rights to it? Or, now that there are publishers involved are there rights right left and centre?

I ask as I wonder if there are other options available? You obviously have a lot of time and money expended in this publication and as yet have seen a zero return.

Those guys will all be at SAR West in Phoenix, AZ this weekend. Anyone who attends, (unfortunately, I haven't been for three years now), should hit them up about the Bren book. We should have tasked our retired Royal Navy compadre Peter! I never thought to ask him to ask Dan WTF is up with it! Neither he or Robert were at Knob Creek or I would have accosted them for sure.

Quote:

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Originally Posted by Peter Laidler

To be really honest Lima, you are asking the same question that Armourers have been asking since pontius was a pilot! The truth is that while there was a theoretical dimensional sequence, it really bore no relation to numbering as we know it on this planet.

This is what we all had in our workshops and I'm sure Tankie, Son and Skippy will (hopefully) agree with. We had a large partitioned tray and the locking shoulders were placed into the relevant partition based entirely on their measured LENGTH and NOT on the size indicated on the underside.

I suggest that you get a selection of locking shoulders, forget the number thereon and select the one that gives the correct CHS of between .064" and .074". You won't need to have one ground as they are fairly easy to stone given a bit of care - or better still, and don't tell anyone I told you, but just stone the rear of the breech block locking bent to suit

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Confimed: L/Shoulders were indeed, held in a multi section wooden tray. As Peter has stated. You selected one & measured it yourself. You NEVER trusted the marked size! The size stamp was merely a starting point most of the time.0.10 thou is a lot to play with TBH. & if you are careful, stoning is straightforward, & relatively easy.
Work to a maxim of Mine: 'You can always take it away, but you cant put it back' (Regarding metal)
Of course you COULD put metal back with weld deposit. BUT, in this HIGHLY stressed & critical area. ANY heat from welding by whatever method. Is a No-No!.....:eek

A point of interest: All 7.62mm L4 Bren series, locking shoulders. were marked with the numerals: 7.62
This was to confirm that they were proofed tested for the breech pressures of the N.A.T.O 7.62mm Cartridge. (so the 'Book' stated. (E.M.E.RS)
wether they actually HAD been. was always a point of conjecture!......:ugh:

Quote:

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Originally Posted by tankhunter

Work to a maxim of Mine: 'You can always take it away, but you cant put it back' (Regarding metal)
Of course you COULD put metal back with weld deposit. BUT, in this HIGHLY stressed & critical area. ANY heat from welding by whatever method. Is a No-No!.....:eek

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Tankhunter,

I was faced with this problem. I chose to make a new locking shoulder and heat treat it. It is necessary to have a good fit into the recess so that the recoil force is transferred directly to the receiver and not through the screw that holds it in place.

Joe