I have an old warhorse, a Russian M-44 carbine chambered for the 7.62x54R cartridge. The bore slugs 0.314" except for the last 1/2" or so at the muzzle, then it opens to 0.317". It shoots "OK", but I'm thinking it could be better without the muzzle wear. Is it possible to counterbore the muzle to eliminate the oversize portion without dismounting the barrel or other dramatics?