5.5645mm NATO – Wikipedia, the free encyclopedia

5.5645mm NATO

5.5645mm NATO with measurement, left to right: bullet, empty case, complete round with bullet in case

The 5.5645mm NATO (official NATO nomenclature 5.56 NATO) is an intermediate cartridge developed in the United States and originally chambered in the M16 rifle. Under STANAG 4172, it is a standard cartridge for NATO forces as well as many non-NATO countries.[3] It is derived from, but not identical to, the .223 Remington cartridge.

In the 1950s, the 7.6251mm NATO rifle cartridge (sold commercially as the .308 Winchester rifle cartridge)[4] was selected to replace the .30-06 Springfield as the standard NATO rifle cartridge. At the time of selection, there had been criticism that the 7.6251mm NATO was too powerful for lightweight modern service rifles, causing excessive recoil, and that the ammunition did not allow for sufficient rate of fire in modern combat.[citation needed]

The British had extensive evidence with their own experiments into an intermediate cartridge since 1945 and were on the point of introducing a .280 inch (7mm) cartridge when the selection of the 7.6251mm NATO was made. The FN company had also been involved.[5] The concerns about recoil and effectiveness were effectively overruled by the US within NATO, and the other NATO nations accepted that standardization was more important at the time than selection of the ideal cartridge.([6]The EM-2, Rifle No.9 Mk1 or "Janson rifle", was an experimental British assault rifle briefly adopted by British forces in 1951, but the decision was overturned very shortly thereafter by Winston Churchill's incoming government in an effort to secure NATO standardisation of small arms and ammunition in the face of American intransigence.) However, while the 7.6251mm NATO round became NATO standard, the US was already engaged in research of their own, which ultimately led to the 5.5645mm NATO cartridge.[citation needed]

During the late 1950s, ArmaLite and other U.S. firearm designers started their individual Small Caliber/High Velocity (SCHV) assault rifle experiments using the commercial .222 Remington cartridge. When it became clear that there was not enough powder capacity to meet U.S. Continental Army Command's (CONARC) velocity and penetration requirements, ArmaLite contacted Remington to create a similar cartridge with a longer case body and shorter neck. This became the .222 Remington Special. At the same time, Springfield Armory's Earle Harvey had Remington create an even longer cartridge case then known as the .224 Springfield. Springfield was forced to drop out of the CONARC competition, and thus the .224 Springfield was later released as a commercial sporting cartridge known as the .222 Remington Magnum. To prevent confusion among all of the competing .222 cartridge designations, the .222 Remington Special was renamed the .223 Remington. With the U.S. military adoption of the ArmaLite M16 rifle in 1963, the .223 Remington was standardized as the 5.5645mm NATO. As a commercial sporting cartridge the .223 Remington was introduced in 1964.

The 5.5645mm cartridge, along with the M16 rifle, were initially adopted by U.S. infantry forces as interim solutions to address the weight and control issues experienced with the 7.6251mm round and M14 rifle. In the late 1950s, the Special Purpose Individual Weapon program sought to create flechette rounds to allow troops to fire sabot-type projectiles to give a short flight time and flat trajectory with a muzzle velocity of 1,200 metres per second (3,900ft/s) to 1,500 metres per second (4,900ft/s). At those speeds, factors like range, wind drift, and target movement would no longer affect performance. Several manufacturers produced varying weapons designs, including traditional wooden, bullpup, "space age," and even multi-barrel designs with drum magazines. All used similar ammunition firing a 1.8mm diameter dart with a plastic "puller" sabot filling the case mouth. While the flechette ammo had excellent armor penetration, there were doubts about their terminal effectiveness against unprotected targets. Conventional cased ammunition was more accurate and the sabots were expensive to produce. The SPIW never created a weapons system that was combat effective, so the M16 was retained, and the 5.56mm round was kept as the standard U.S. infantry rifle cartridge.[5]

In a series of mock-combat situations testing in the early 1960s with the M16, M14 and AK-47, the Army found that the M16's small size and light weight allowed it to be brought to bear much more quickly.[citation needed] Their final conclusion was that an 8-man team equipped with the M16 would have the same fire-power as a current 11-man team armed with the M14.[citation needed] U.S. troops were able to carry more than twice as much 5.5645mm NATO ammunition as 7.6251mm NATO for the same weight, which would allow them a better advantage against a typical NVA unit armed with AK-47, AKM or Type 56 assault rifles.

(*AK-47/AKM magazines are much heavier than M14 and M16 magazines)

In 1977, NATO members signed an agreement to select a second, smaller caliber cartridge to replace the 7.6251mm NATO cartridge.[9] Of the cartridges tendered, the 5.5645mm NATO was successful, but not the 55gr M193 round used by the U.S. at that time. The wounds produced by the M193 round were so devastating that many[10] consider it to be inhumane.[11][12] Instead, the Belgian 62gr SS109 round was chosen for standardization. The SS109 used a heavier bullet with a steel tip and had a lower muzzle velocity for better long-range performance, specifically to meet a requirement that the bullet be able to penetrate through one side of a steel helmet at 600 meters. This requirement made the SS109 (M855) round less capable of fragmentation than the M193 and was considered more humane.[13]

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