NATO's 7.62 × 51 mm rifle cartridge, commercially known as .308 Winchester, was introduced in the 1950s as a standard firearm cartridge among NATO countries, though it has also become popular among civilians. The round is produced by many manufacturers in types that include tracers and blanks.
The military 7.62 × 51 mm is nearly identical to the commercial .308 Winchester. NATO controls specifications for the military round while SAAMI controls specifications for the civilian round. The organizations have established two differences: the standard pressure is 50,000 psi for most military rounds, while the SAAMI maximum is 62,000 psi for the civilian round. The NATO M60 High Pressure Test round, is loaded to a pressure of 67,500 psi, so military arms should be capable of handling the pressure of civilian rounds. The military chamber is specified to be 1.645 inches, compared to the civilian chamber of 1.632 inches, a difference of just 0.013 inches, but a chamber at the long end of acceptable military length will put excessive stress on the thinner civilian brass, causing premature head separation. To summarize, while it is not unsafe to mix .308 and 7.62 x 51 mm ammunition, fewer problems will be encountered if the correct caliber designation is used.
The cartridge was introduced to military service in rifles and machine guns. It was used in the M14 rifle and M60 machine gun in U.S. service in the late 1950s. Fabrique Nationale's FAL became the most popular 7.62 NATO rifle in Europe and served into the early 1980s. The M14 was superseded in U.S. service as the infantry adopted a new round with the M16. However, the M14 and many other firearms that use the round remain in service. The round is used by infantry and from ground vehicles, aircraft and ships. It is used in the GE M134 Minigun as well.
The round itself offers similar ballistic performance in most firearms to the round it replaced in U.S. service, the .30-06 Springfield. While the cartridge itself is shorter, the actual bullet and loadings are about the same (muzzle velocities on the order of 860 m/s (2,800 ft/s) for both). The smaller case uses less brass and firearms that use the round can be smaller (for a similar example, compare .45 GAP and .45 ACP), but the reduced size limits flexibility in civilian use, hindering performance with heavier bullets and slower-burning, lower-density powders (see internal ballistics).
The development work that would eventually develop into the 7.62 × 51 mm started just after World War I, when it became clear that the long cartridge of the U.S. standard .30-06 round made it difficult to use in semi- and fully automatic weapons (the .30-06 was in turn derived from an earlier .30-03 cartridge), and had more case capacity than was needed. A "shorter" round would allow the firing mechanism to be made much smaller, and improve the feeding, both of which would allow for higher rates of fire. At the time one of the most promising designs was the .276 Pedersen, but in 1932 it was rejected with an Army recommendation that only rounds of .30 inch (7.62 mm) would meet requirements.
Thus when the war appeared to be looming again only a few years later, the .30-06 was the only round available. Nevertheless the U.S. Army did use it to great effect in the M1 Garand, which provided U.S. troops with considerably higher firepower than most of their bolt-action-armed opponents. The Garand performed so well that the U.S. saw little need to replace it until almost a decade later, and the .30-06 remained in service well beyond the Korean War and into the 1960s.
During the 1940s and early 1950s several experiments were carried out to improve on the Garand. One of the most common complaints was the difficulty in reloading the weapon using its "en bloc" clips, and many experimental designs modified the weapon with a detachable box magazine. One of these, Springfield Armory's T20, was a fully automatic version. The U.S. Army finally found this design to be worthy enough to consider replacing the Garand, and decided it was also time to look at improved ammunition once again.
The test program continued for several years, including both the original .30-06 round and a modified .300 Savage (then known as the T65). In the end, the T65 design demonstrated power roughly equal to the original .30-06, firing a 147-grain bullet at 2,750 feet per second, while being somewhat shorter and much more reliable in feeding. The T44, an adaptation of the T20 to fire the new round, was the almost-uncontested winner of the competition.
When the U.S. announced its intentions to introduce the T65, the British were incensed. They had considerable evidence to demonstrate that their own .303 British could not be controllably fired in a shoulder-fired automatic rifle, and the somewhat more powerful T65 would be even harder to control. They had spent considerable time and effort developing an intermediate-power round, the .280, to solve these problems. The U.S. countered with its pre-WWII requirements that stated that only a .30-caliber design would do. After considerable squabbling between the two armed forces, the argument was settled in unlikely fashion when the Canadian Army announced they would be happy to use the .280, but only if the U.S. did as well — a tacit agreement to use the T65, as it was clear the U.S. would not use the .280. The T65 was chosen as the NATO standard in 1954.
The T44 was adopted as the M14 in 1957. Britain and Canada began receiving FN FALs around the same time, as the West German army adopted a modified version of the Spanish CETME rifle, as the Heckler & Koch G3. However it was not long before those involved realized the British had been right all along, the .308 could not reliably be fired in full-auto due to recoil. M14s were later delivered with the full-auto selection locked out, and adaptations to the FAL to allow it included the addition of a bipod and heavier barrel.
While all of this was going on, the U.S. Project SALVO had concluded that a burst of four rounds into a 20-inch circle would cause twice the number of casualties as a full-auto burst by one of these "battle rifles" — regardless of the size of the round. They suggested using a much-smaller .22 caliber cartridge with two bullets per cartridge (a "duplex load"), while other researchers investigated the promising flechette rounds that were even lighter but offered better penetration than even the .30-06. These studies were kept secret in case the British found out about them and used that as evidence in favour of their smaller rounds.
When the M14 arrived in Vietnam with U.S. troops, it was found to be ungainly. The rifle's length and weight were poorly suited for jungle warfare. Troops were less able to compete with the maneuverable AK-47. Also, the larger rounds were heavy, limiting the amount of ammunition that could be carried.
Fighting between the big-round and small-round groups reached a peak in the early 1960s, when test after test showed the "puny" .223 Remington round fired from the AR-15 allowed an 8-soldier unit to vastly outgun an 11-soldier unit armed with M14s, and beat the typical NVA unit armed with AK-47s. In 1964, the U.S. Army started replacing their M14s with the M16, incurring another series of complaints from the UK Government. However a large number of troops preferred the M14, because of its power, and because it was more durable than the M16.
Regardless of being poorly suited for jungle warfare. 7.62 × 51 mm rifles stayed in military service around the world due to several factors. The 7.62 mm NATO has proved much more effective than 5.56 × 45 mm NATO at long ranges, and has since found popularity as a sniping round. For instance, M14 variants are still used in the United States military as designated marksman and sniper rifles. Shorter, more maneuverable 7.62 mm rifles like the Heckler & Koch G3 stayed in service due to their accuracy, range, power, and reliability.
The 7.62 mm nevertheless met the designer's demands for full-auto reliability with a full-power round. It remained the main squad machine gun round for almost all NATO forces well into the 1990s, even being used in adapted versions of older .30-06 machine guns such as the Browning M1919A4 from the WWII era. These too have been replaced to some extent by .223 weapons, such as the widespread FN Minimi, but they remain the primary armament on most flexible mountings such as helicopters, jeeps, and tanks.
Winchester saw the market for a civilian model of the T65 round in 1952, which to this day remains popular as the .308 Winchester game round. The cartridge is very popular with American sportsmen both for long-range target shooting and hunting big game up to the size of elk or moose.
Firearms using the 7.62 × 51 mm NATO round
Kalashnikov-pattern Saiga firearms
FRF2 sniper rifle
Heckler & Koch G3 rifle
Heckler & Koch PSG1 sniper rifle
Lee-Enfield L8 series rifles
L42A1 sniper rifle
Enfield Enforcer rifle
L96A1 Sniper rifle
M21 sniper rifle
M25 sniper rifle
M24 sniper rifle
M40A1 and M40A3 sniper rifles
M60 machine gun
M240 machine gun
M1919A4 machine gun
MG3 machine gun
Mk 48 Mod 0 machine gun
Israeli Mauser Kar-98k rifle
Remington Model 7600 rifle
Remington Model 700 rifle
Steyr Scout rifle
Type 62 Machine gun
Type 64 rifle
Winchester Model 70 rifle