(In reference to GC 2 and GC 3, this term was used to describe the type of Ammo used)
The 7.62×51mm NATO (official NATO nomenclature 7.62 NATO) is a rifle cartridge developed in the 1950s as a standard for small arms among NATO countries (not to be confused with the similar 7.62x54mmR cartridge). When loaded with a bullet design that expands, tumbles, or fragments in tissue, this cartridge is capable of delivering very effective terminal performance. Proponents of the hydrostatic shock theory contend that this includes remote wounding effects known as hydrostatic shock.
It was introduced in U.S. service in the M14 rifle and M60 machine gun in the late 1950s. The M14 was superseded in U.S. service as the infantry adopted the 5.56x45mm NATO M16. However, the M14 and many other firearms that use the 7.62×51 round remain in service, especially in the case of sniper rifles, machine guns, and as the service weapon chosen by special operations forces. The cartridge is used both by infantry and on mounted and crew-served weapons mounted to vehicles, aircraft and ships.
Although not identical, the 7.62×51mm NATO cartridge is similar enough to the commercial .308 Winchester that the Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) considers it safe to fire the NATO round in weapons chambered for the commercial round.