I have an M-44 Ruskie carbine I acquired. The bore is dark and somewhat pitted, but is accurate at a 100yds with no overpressure signs. Are the bores usually so crude-looking or did I get a crummy interior?
Maybe some Russian soldier was too busy shooting Germans to keep his rifle clean and corrosive primers did the rest. That's the darn trouble with war, too hard on nice weapons!
Lap the barrel. Slug it and use the largest diameter bullet you can. I think you will end up needing a .311 to get better accuracy. Of course you may have to reload to get the round you need.