7.62 x 51 mm NATO

7.62×51mm NATO
7.62×51mm NATO rounds compared to AA (LR6) cell.
Type	Rifle
Place of origin	United States
Service history
In service	1954–present
Used by	United States, NATO, others.
Wars	Vietnam War, Six-Day War, Yom Kippur War, Falklands Conflict, The Troubles, Gulf War, War in Afghanistan, Iraq War, Libyan Civil War, Syrian Civil War, Yemeni Civil War (2015-present), Saudi-led intervention in Yemen, among other conflicts
Specifications
Parent case	.308 Winchester (derived from the .300 Savage)
Case type	Rimless, Bottleneck
Bullet diameter	0.308 in (7.82 mm)
Neck diameter	0.345 in (8.8 mm)
Shoulder diameter	0.454 in (11.5 mm)
Base diameter	0.470 in (11.9 mm)
Rim diameter	0.473 in (12.0 mm)
Rim thickness	0.050 in (1.3 mm)
Case length	2.015 in (51.2 mm)
Overall length	2.750 in (69.9 mm)
Rifling twist	1 in 12 in (304.8 mm)
Primer type	Large Rifle
Maximum pressure (NATO EPVAT)	60,191 psi (415.00 MPa)
Ballistic performance
Bullet mass/type Velocity Energy 147 gr (10 g) M80 FMJ 2,733 ft/s (833 m/s) 2,437 ft·lbf (3,304 J) 175 gr (11 g) M118 Long Range BTHP 2,580 ft/s (790 m/s) 2,586 ft·lbf (3,506 J)
Test barrel length: 24 inches (61 cm) Source(s): M80: Slickguns, M118 Long Range: U.S. Armorment

The 7.62×51mm NATO (official NATO nomenclature 7.62 NATO) is a rimless bottlenecked rifle cartridge developed in the 1950s as a standard for small arms among NATO countries. It should not be confused with the similarly named Russian 7.62×54mmR cartridge, a slightly longer rimmed cartridge.

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 The M14 was superseded in U.S. service as the infantry adopted the 5.56×45mm NATO M16. However, the M14 and many other firearms that use the 7.62×51 round remain in service, especially in the case of various sniper rifles, medium machine guns such as the M240, and various rifles in use 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 and the commercial .308 Winchester cartridges are similar enough that they can be loaded into rifles chambered for the other round, but the Winchester .308 cartridges are typically loaded to higher pressures than 7.62×51mm NATO cartridges. Even though the Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) does not consider it unsafe to fire the commercial round in weapons chambered for the NATO round, there is significant discussion about compatible chamber and muzzle pressures between the two cartridges based on powder loads and wall thicknesses on the military vs. commercial rounds. While the debate goes both ways, the ATF recommends checking the stamping on the barrel; if one is unsure, one can consult the maker of the firearm.

The 7.62x51mm offers the same ballistic performance as the original 1906 load for the .30-06 Springfield, the cartridge it replaced in U.S. service. Modern propellants allowed for similar performance from a smaller case with less capacity, a case that requires less brass and yields a shorter cartridge. This shorter cartridge allows a slight reduction in the size and weight of firearms that chamber it, and somewhat better cycling in automatic and semi-automatic rifles.