However, in practical terms, a velocity drop of say 100 fps at the muzzle and minor accuracy degradation when firing .223 Remington ammunition in a 5.56 NATO-chambered rifle are largely irrelevant ...
The M855A1, a 5.56 mm Ball ammunition, is an enhanced performance round for today’s combat and training environments. It works with the M4 Carbine, the M249 machine gun, and the H&K and M16A2 ...