I shoot .311 Sierra bullets in my old Jap rifle which is supposed to be 31 caliber. But Hornaday uses .312 for it. I have seen everything from .311, .312, .313, .321 and .323 called 32 caliber. Many call the 7.7 a 31 caliber others a 32 caliber. Man can someone sraighten this out?

Hi: I had one years ago, but forget...although I
think the bore is the same as a .303 Brit or .312.
There may be variations too, why not just "slug"
the bore with soft lead? Even a partial slugging
at the muzzle, then driving it out with a cleaning rod from the breech will give you a pretty close
measurement. My book gives .312 for the 7.7 Jap.
You can get pretty good velocities from reloading this cartridge...its not bad, in fact a pretty good one. Aloha, Tom

Yeah Bisonland I am shooting 3/8 groups with the .311 bullets and was wondering if the tighter .312 might do as good or better. Slugging the barrel sounds like the thing to do.

Hi: I think (if my memory serves me) that the
bores of the 7.7 vary somewhat & are actually
larger than the specifications listed...
I'm sure I slugged mine & found a larger
diameter bore. P.O. Ackley has stated that
bullets from .312-.314 are used. I got real
good velocity in my 7.7, but was years ago &
just only remember the velocity was really
good with reloads...also accurate.
Best Regards, Tom