5.56x45mm NATO

The 5.56x45mm NATO is a rimless, bottlenecked, centerfire intermediate rifle cartridge developed in the late 1970s in Belgium by FN Herstal, encompassing the SS109, L110 and SS111 loadings. On 28 October 1980 it was standardized under STANAG 4172 as the second standard service rifle cartridge for NATO forces, and it is also used by many non-NATO countries. The cartridge family was derived from the .223 Remington round designed by Remington Arms in the early 1960s, sharing a near-identical case, though chamber dimensions differ slightly between rifles built for each cartridge. Firing 5.56mm NATO ammunition in a rifle chambered only for .223 Remington can produce unsafe chamber pressures, so the two are not considered interchangeable.