5.56 NATO

**5.56x45mm NATO** is the standard service rifle cartridge of the U.S. military and most of the Western world. It feeds the M4, M16, and the enormous civilian AR-15 platform. 5.56 is not the same as its civilian cousin **.223 Remington**, though the difference matters more in direction than in practice: a rifle chambered in 5.56 will safely shoot .223, but not the other way around. Civilian rifles are commonly chambered in "5.56 NATO" or the hybrid **.223 Wylde** to accept both. It's light, flat-shooting inside 300 yards, and inexpensive enough to train with in volume. For most civilian shooters it represents the best ratio of hit probability to recoil to cost in a rifle cartridge — which is why the AR-15 ecosystem built around it is the size it is.