5.56x45 NATO Round

5.56x45 NATO

The 5.56x45mm NATO cartridge is a rimless bottlenecked intermediate cartridge developed in the late 1970sand early 1980's. It's the second standard service rifle cartridge used for the NATO forces, adopted under STANAG 4172 in 1980. It was derived from the .223 Remington, a very similar round, and while not identical, it's often referred to as the "five-five-six".