Thanks for the replies. I should have mentioned that it is indeed a 91/30, from 1939 (Don't know if the year affects anything). The ammo I am currently using is definitely surplus, not sure where it is from exactly though... I think it is russian milsurp ammo. As for the cosmoline, i disassembled the entire thing, and soaked all the small parts in mineral spirits for a day, and sprayed brake degreaser all over the inside and outside and wiped everything down pretty good. Maybe I should do it again?
the year really does not matter all that much with 91/30s. the main differentiation are hexagonal receivers and round receivers, HEX are more sought after but there is nothing wrong with the round receivers, just more of them around I guess. if you bathed it in mineral spirits then a second time will probably yield very little. I would recommend buying a box of modern production ammo, wolf isn't too much more expensive than surplus anymore so it would be a nice control group. if it works fine then the ammo is just oversized, if it is still a tight fit then you either have poor head spacing or still gunk in the chamber, either way you know it's a problem with the gun or ammo.