| 7.62×51mm NATO | ||
|---|---|---|
7.62×51mm NATO rounds compared to AA (LR6) battery. |
||
| Type | Rifle | |
| Place of origin | United States | |
| Service history | ||
| In service | 1954–present | |
| Used by | United States, NATO, others. | |
| Wars | Vietnam War, Falklands Conflict, The Troubles, Gulf War, War in Afghanistan, Iraq War, 2011 Libyan civil war | |
| Specifications | ||
| Parent case | .308 Winchester (derived from the .300 Savage) | |
| Case type | Rimless, Bottleneck | |
| Bullet diameter | 7.82 mm (0.308 in) | |
| Neck diameter | 8.77 mm (0.345 in) | |
| Shoulder diameter | 11.53 mm (0.454 in) | |
| Base diameter | 11.94 mm (0.470 in) | |
| Rim diameter | 12.01 mm (0.473 in) | |
| Rim thickness | 1.27 mm (0.050 in) | |
| Case length | 51.18 mm (2.015 in) | |
| Overall length | 69.85 mm (2.750 in) | |
| Rifling twist | 1:12" | |
| Primer type | Large Rifle | |
| Maximum pressure | 415 MPa (60,200 psi) | |
| Ballistic performance | ||
| Bullet weight/type | Velocity | Energy |
| 9.7 g (150 gr) FMJ | 850 m/s (2,800 ft/s) | 3,504 J (2,584 ft·lbf) |
| 11.3 g (174 gr) M118 Long Range BTHP | 790 m/s (2,600 ft/s) | 3,526 J (2,601 ft·lbf) |
| Source(s): Popenker,[1]FMJ Info from Olive Drab,[2] M118 Long Range BTHP Info from usarmourment.com [3] | ||
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 similarly named Russian 7.62x54mmR 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 The M14 was superseded in U.S. service as the infantry adopted the 5.56x45mm NATO M16.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.[4]
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The cartridge itself offers similar ballistic performance in most firearms to the .30-06 Springfield that it replaced in U.S. service. Though shorter, standard loadings fire similar bullet weights at similar velocities. Modern propellants allowed the same velocity from a case with less capacity. The smaller case requires less brass and yields a shorter cartridge. This shorter cartridge allows a reduction in the size of the firearms that chamber it. Proponents of the hydrostatic shock theory contend that the difference affects remote wounding characteristics known as hydrostatic shock.[5][6][7]
Work that would eventually develop the 7.62×51mm NATO started just after World War I when the large, powerful .30-06 cartridge proved difficult to adapt to semi-automatic rifles. A less-powerful cartridge would allow a lighter firing mechanism. At the time the most promising design was the .276 Pedersen. When it was eventually demonstrated that the .30-06 was suitable for semi-automatic rifles, the .276 was dropped.
Thus when war appeared to be looming again only a few years later, the .30-06 was the only round available and the M1 Garand provided US troops with greater firepower than their bolt action-armed opponents. The Garand performed so well that the US saw little need to replace it during World War II and the .30-06 served 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 limited capacity en-bloc clip and many experimental designs modified the weapon with a detachable box magazine. Springfield Armory's T20 rifle, was a fully automatic version. Though not adopted, experience with a fully automatic Garand laid the groundwork for its replacement.
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 cartridge demonstrated power roughly equal to the original .30-06, firing a 147-grain bullet at 2,750 feet per second (840 m/s) but was approximately half an inch shorter. The eventual result of this competition was the T44 rifle.
When the United States developed the T65 cartridge, the British took a different route. They had spent considerable time and effort developing the intermediate-power .280 British (7 mm) cartridge with an eye towards controllable fully automatic fire. Meanwhile, the US held to its desire not to reduce the effectiveness of individual shots. The American philosophy was to use automatic fire for emergencies only and continue to use semi-automatic fire the majority of the time. After considerable debate the Canadian Army announced they would be happy to use the .280 but only if the U.S. did as well. It was clear the U.S. would not use the .280. Although the British did start introducing the .280 along with the "bull-pup" Rifle No. 9, the process was stopped in the interests of harmonization across NATO. The T65 was chosen as the NATO standard cartridge in 1954.
The T44 was adopted as the M14 in 1957. Britain and Canada adopted the Belgian FN FAL around the same time followed by West German army as the G1. The Germans soon transitioned to a modified version of the Spanish CETME rifle, Heckler & Koch G3. With all three of these firearms, it was clear that the 7.62mm NATO could not be fired controllably in fully automatic due to recoil. Both the M14s and FAL would later go through several variations intended to either limit fully automatic selection through semi-auto version or selector locks or improve control with bipods and/or heavier barrels.
While all of this was going on, the U.S. Project SALVO concluded that a burst of four rounds into a 20-inch (510 mm) circle would cause twice the number of casualties as a fully automatic 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 to prevent the British from using them as evidence in favour of their smaller rounds.
When the M14 arrived in Vietnam, it was found to have a few disadvantages. The rifle's overall length was not well suited for jungle warfare. Also, the weight of 7.62×51mm cartridges limited the total amount of ammunition that could be carried when compared with the common 7.62×39mm cartridge of the Type 56 assault rifles, which the Vietcong and North Vietnamese Army soldiers were equipped with. In addition, the originally issued wooden stocked versions of the M14 were susceptible to warping from moisture in tropical environments, producing "wandering zeroes" and other accuracy problems (this was fixed with the adoption of fiberglass stocks).
Fighting between the big-round and small-round groups reached a peak in the early 1960s, when test after test showed the .223 Remington cartridge fired from the AR-15 allowed an 8-soldier unit to outgun an 11-soldier unit armed with M14s. U.S. troops were able to carry more than twice as much 5.56×45mm ammunition as 7.62x51mm for the same weight, which would allow them a better advantage against a typical NVA unit armed with AK-47s.
| Rifle | Cartridge | Cartridge weight | Weight of loaded magazine | 10 kilogram ammo load |
|---|---|---|---|---|
| M14 | 7.62×51mm | 393 gr | 20 rds @ .68 kg | 14 mags / 280 rds |
| M16 | 5.56×45mm | 183 gr | 20 rds @ .3 kg | 33 mags / 660 rds |
| AK-47 | 7.62×39mm | 281 gr | 30 rds @ 1.2 kg*[8] | 8 mags / 240 rds |
(*AK-47 magazines are much heavier than M14 and M16 magazines)
In 1964, the U.S. Army started replacing their M14s with the M16, incurring another series of complaints from the British. Regardless of the M14 having disadvantages in jungle warfare, 7.62×51mm NATO rifles stayed in military service around the world due to several factors. The 7.62×51mm NATO has proved much more effective than 5.56×45mm at long ranges, and has since found popularity as a sniping round. For instance, M14 variants such as the Mk 14 Mod 0 Enhanced Battle Rifle and M21 are still used in the United States military as designated marksman and sniper rifles. Shorter, easier to handle 7.62mm rifles like the Heckler & Koch G3 stayed in service due to their accuracy, range, cartridge effectiveness and reliability.
The 7.62×51mm NATO round nevertheless met the designer's demands for fully automatic reliability with a full-power round. It remained the main 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 have been replaced to a considerable extent in the light machine gun role by 5.56×45mm NATO weapons, such as the widespread use of the FN Minimi, but the 7.62 round is still the standard chambering for most general-purpose machine guns such as the FN MAG and the German MG3, and flexible mountings such as helicopters, jeeps, and tanks.
Winchester Ammunition (a division of the Olin Corporation) saw the market for a civilian model of the T65 cartridge and released it commercially in 1952 as the .308 Winchester, two years prior to adoption of the cartridge by NATO.