A mosin 91/30 can't shoot 7.62x51mm NATO rounds without being damaged, because the bullet is a bit smaller and the cartridge case is a bit shorter than the 7.62x54mmR. If you want to shoot a 7.62x51mm round with the mosin u need to change the barrel, the bolt and also the internal magazine. As fare as i know thats nearly impossible to do and if the game is going to strive to realism the description should be changed.