You'll probably want to slug the bore. Mine is 0.313" but shoots Hornady 174gr .312 bullets well.
If your gun is a rechambered 7.7 it will probably shoot .308 bullets okay (if 3-4" at 100 yards is acceptable). If it was mine I'd load .312 bullets in .30-06 cases.
If you load .312 bullets MAKE SURE the neck area of the chamber is not pinching the loaded cartridge by painting a loaded round with magic marker and inspecting it for drag marks and such after chambering it a couple of times. Arisakas are tough, but not that tough.
Proud member of the NRA and Texas State Rifle Association. Registered and active voter.