Its very similar to my British ammo tin for 7.62mm machine gun ammunition. This is outside my area of knowledge but this type may well be in use with other NATO countries.
Looks like a US .30 cal, for M-60 machine gun ammo. I think they still use it for the M 240 G ammo
47th MP Co/47th Inf Div 1983-1988
583rd Ord Co 59th Ord Bde Muenster, W Germany
Looking for P37 ammo pouch with No4 bayo frog