ballistics

7.62 x 51mm Nato
800–1,000 m max, most penitration/stopping power power 600m apparantly,
designed marksman 800m max with G3 Battle rifle, 6x scope

500yards, 1753 fps, 1576 ft lbs
nominal, 2700 fps, 2427 ft lbs

5.56 x 45mm Nato
400–600 m, half accurate at 400m than 7.62, power falls beyond 200m

500yards, 648 fps, 252 ft lbs
nominal, 3185 fps, 1239 ft lbs

The original ak47 has a destinctive sound because it fires russian caliber and charge size.

7.62 x 39mm Ak47
500yards, 622 fps, 414 ft lbs
nominal, 1598 fps, 2400 ft lbs