What is the standard round used in the M16A2 and M4 series weapons?

The standard round used in the M16A2 and M4 series weapons is indeed the 5.56mm ball, M855. This round was specifically designed to meet the requirements of the U.S. military for use in these firearms. It features a boat-tail design for improved aerodynamics and accuracy. The M855 cartridge is a NATO standard round that offers adequate performance in various combat scenarios, delivering both velocity and effective terminal ballistics at typical engagement ranges for infantry operations.

The selection of this round is integral to maximizing the operational effectiveness of the M16A2 and M4 platforms, as it is optimized for their rifled barrels and designed to maintain effective performance in both close and sustained engagements. The design considerations of the M855, including its ability to penetrate soft body armor, make it particularly useful in modern combat situations.

On the other hand, the other options represent different calibers or types of ammunition that are not standard for the M16A2 and M4 series. The 7.62mm M80 is used in different weapons, akin to heavier rifles. The 9mm M882 is typically associated with handguns and submachine guns, while the 5.45mm M855A1, though it resembles the