Muzzle counterbore diameter?

[gamachinist]

Hello oh learned ones,

I had a request from someone on another board to shorten or counterbore a rifle barrel (No.4Mk1 SMLE).

Depth is no question,just deep enough to get to good rifling again,if possible.

My question is,how large in diameter to counterbore?
I don't have a No.4 out of the safe,but the No.1 MkIII barrel I measured was .560" od.
Does anyone have one of the Garands that was counterbored to give me an idea what size to bore to,or just previous experience to go by?

Thanks,Robert.

 

[Jim K]

.360-.370 should do OK, or 3/8 (.375) if you only have fractional drills. But do it in a lathe; if the counterbore is not perfectly even it will act just like an uneven crown and throw bullets all over.

The No. 4 barrel runs .595+ at the muzzle. so you have a bit more room than with the No.1 Mk III.

Jim

 

[gamachinist]

Thanks Jim,
I was thinking of making a long pilot to use on a counterbore for socket head bolts.I have a floating reamer holder to hold it with in the lathe tailstock too.
Opinion?
Regards,Robert.

 

[Jim K]

I had a hollow headstock, so with something like that I just took the barrelled action out of the stock and chucked up the barrel. Then I chucked a drill in the tailstock. But anything that can cut the counterbore even should be OK. A reamer might be OK, as long as the pilot is bore size.

Jim