Hornady Frontier 5.56x45mm NATO 55gr. FMJ M193 Rifle Ammo – 20 Rounds FR200 Caliber: 5.56x45mm NATO, Number of Rounds: 500,The 5.56 for sale ×45mm NATO (official NATO nomenclature 5.56 NATO, fyv-FYV-six) is a rimless bottlenecked intermediate cartridge family developed in the late 1970s in Belgium by FN Herstal. It consists of the SS109, SS110, and SS111 cartridges. On 28 October 1980 under STANAG 4172 it was standardized as the second standard service rifle cartridge for NATO forces as well as many non-NATO countries. Though they are not entirely identical, the 5.56×45mm NATO cartridge family was derived from and is dimensionally similar to the .223 Remington cartridge designed by Remington Arms in the early 1960s.