Bullet Base Markings

Hi, All…Awhile back, we had a thread or two concerning bullet base markings. If anyone is still interested, we found a fired bullet on the range yesterday with an M on the base. Bullet measures .310"-.311" at base, weighs 153 grains, appears to be solid GM (no lead at all), non-magnetic. Four non-knurled narrow cannelures on bullet, fired from a weapon with six narrow rifling lands. Nose of bullet badly deformed from impact so can’t comment on original shape except to say more than likely spitzer. 7.62 x 54R Russian ??..Randy