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 rifles.

Does the military use 223 or 556?

The US military has been using the 5.56 mm round for nearly 60 years — here's how it all got started. While the Army is currently planning to move away from the 5.56 mm round in its infantry weapons, that has been the standard for decades.

Is 5.56 or 7.62 better?

So, returning to the metrics of power, accuracy, and recoil, the 7.62 round wins the first category, but the 5.56 takes the second two, making it the apparent winner. ... There are good reasons to run each, but for most shooters, the 5.56 round is the better choice for faraway targets.