Help with .308 NATO headstamp

Hi: First post here. I’m a rimfire guy but a friend gave me a .308 cartridge and was wondering about the headstamp. I don’t know anything other than I suspect that it is a NATO round. The headstamp has that small crosshair in a circle at the top above the primer. Below the primer the stamp is: FNM 82-31. There are three small square indentations equidistant around and adjacent to the primer. Case appears to have been annealed and the bullet is FMJ.

Any guesses or downright confident answers out there?

Thank you,

Sounds like you have some Portguese surplus 7.62x51mm ammo.

Made by Fabrica Nacional de Muniçoes de Moscavide in Portugal.

That pretty much sums it up! Thank you, gentlemen!