Originally Posted by rwsmith

The slugging is a good idea and I think I'll do it since I have no idea how much it has been shot. (It's a 1937 manufacture) And 7.62 mm does convert to .308" which does work in my American made .30 cal. rifles.

I'm not sure, except for the '3 line' specification (.30 caliber) how the Russians arrived at bullets several thousandths larger than .30 cal.
The whole series of .30 cal rifles included the .303 British, the 7.7mm Arisaka and the 7.62 Mosin, all of which are larger by a few thousandths than .308.

Anything under a 7.92mm, usually referred to as 8mm, seems to be a .30 cal.There doesn't seem to be any .31 caliber cartridges.