Answer: this is a pre-1980 .50 BMG bullet. You can tell because the bullet in question does not have a boat-tail heel, which was a recent development in firearms from the 1980's forward. Most likely fired from a M2 Browning Machine Gun, as these guns would most often see action in the Navy. Although the GAU-19 might be a possible contender, it wouldn't be, because the GAU-19 only fired 50cal with a boat-tail. If you look at the grooves on the bullets, it exhibits a 8 lands and grooves right handed twist, matching the original design of a browning machine gun barrel.