IMHO it was perfect before, but I could accept the following:
Talking only vs heavy armor:
7.62x51 NATO & 7.62x54 R weapons should all kill in 1 shot to the upper chest at least, making taking two to the stomach area to die possible with heavy armour.
5.56 NATO, 7.62x39 & 5.45 Russian should all kill in 2 shots to the upper chest (main difference between 7.62 full power vs AR calibers) as well as stomach.
I think damage should be based on the kinetic energy of the round, it's the only fair way to balance things, and a 168 grain 7.62 round does after all pack noticably bigger punch than any AR round, which should be reflected ingame IMO.
As for bolt action rifles, just give them 7.62 AP ammo and make them 1 shot kills to any part of the body except limbs - albeit a shot to the arm from the side should penetrate through into the torso, but that goes for all rounds.
There's a reason militaries around the world have been reissuing the battle rifle én masse for a while now, the stopping power of the 7.62 was sorely missed by the troops.