5.56×45mm NATO

The 5.56×45mm 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. It is derived from, but is not identical to, the .223 Remington cartridge.

History

In the 1950s, the 7.62×51mm NATO rifle cartridge (physically interchangeable with, but not identical to, the .308 Winchester rifle cartridge) 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 7.62×51mm NATO was too powerful for lightweight modern service rifles, causing excessive recoil, and that as a result it did not allow for sufficient automatic rate of fire from hand-held weapons in modern combat.

The British had extensive evidence with their own experiments into an intermediate cartridge since 1945 and were on the point of adopting a .280 inch (7 mm) cartridge when the selection of the 7.62×51mm NATO was made. The FN company had also been involved in the development of the .280 round including developing a version of the FN FAL in .280. 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. However, while the 7.62×51mm NATO round became NATO standard, the US was already engaged in research of their own, which ultimately led to the 5.56×45mm NATO cartridge.