I’ve often wondered about the slight differences in the way caliber is used.
The 7.62X51 NATO round is I believe identical to the .308 Winchester round.
But converting 7.62mm to inches gives
7.62mm X (1/25.4)in/mm = .3000... in.
I think the difference may be that .308 is the bullet diameter, but .300 (the caliber in European NATO parlance) is the land-to-land diameter of the barrel.
“I think the difference may be that .308 is the bullet diameter, but .300 (the caliber in European NATO parlance) is the land-to-land diameter of the barrel.”
Exactly right. If the bore diameter is .300 and the rifling is .004” deep, then the overall bore diameter from groove-to-groove is .308”. As a reloader, I know that .308 has been popular over the years for a number of commercial and military calibers.