Originally Posted by
Small cog
7.62 is also NATO standard.
7.62 x 51mm is NATO, 7.62 x 39mm is Soviet where 51mm and 39mm refer to the length of the casing. Standard NATO spitzer point, boat-tail, full metal jacket (ball) projectiles are 33.3mm long. The round in the photo is almost certainly a 7.62 x 39mm projectile.