.223 Remington

p>The .223 Remington cartridge is the American equivalent of the 5.56 NATO. Along with the NATO round, the .223 Remington is by far the most widely-used ammunition in AR-15s. It's a very powerful yet low-recoiling round, which makes it a lot of fun for recreational and competitive shooters. It has also been used extensively by the U.S. military as a lighter and easier to carry option than the .308 Winchester round.