My .308/7.62mm fullauto conversion- Plug & Play Success!!

[Syntax Error]

Hi Joe,

That's the thing, it does barely close the bolt with a field gauge (7.62x51 NATO Forster Field gauge, 1.6455", found here: NATO Chamber Headspace Gages - Forster Products), so it's unsafe to shoot normal ammo as it is right now. I guess the "easy" path is swap out locking shoulders (or use an L4 locking shoulder and hope it headspaces) and exclusively shoot .308 out of the gun. I would like to maintain the .303 option, hence maintaining the current locking shoulder and machining the L4 bolt somehow. Is it so hard that even carbide bits won't be able to scratch it? I figure just go very slow and methodical in shaving it down to fit, if I can, on the locking shoulder side as that's less material than the bolt face side.

[tr63]

You really should check your head space on your .303 barrel with the existing locking shoulder . You might have a too large head space now . As you know the .303 round may work in the Bren Gun that is out of spec. head pace .074 max. Who build your Mk II Bren ?

[Joe H]

You really should check your head space on your .303 barrel with the existing locking shoulder . You might have a too large head space now . As you know the .303 round may work in the Bren Gun that is out of spec. head pace .074 max. Who build your Mk II Bren ?

Syntax,

Good point from TR63. The .303 British is very forgiving regarding loose headspace due to the length of its solid head. Not surprising that you have not had any problems with the .303. The 7.62 Nato and 7.62 x54R are much less forgiving.

I put a 7.62 SA barrel on my properly headspaced .303 and it checked out for 7.62 Nato. No problems firing.

The easiest way to fix loose HS is to get or make a longer Locking shoulder and grind back as necessary to get the correct headspace. If I remember correctly the standard length is .812". The LS should be hardened.

Brp has longer ones you can use to to get the correct headspace . You can make a new one, TIG weld 4140 on the face of the old one and grind back, slot the LS and shim the back. You can check your Locking shoulder but I think the grinding angle is 25 deg.

30: Bren Locking Shoulder (specify size 2x or 3x) - BRP CORP

Joe