What size ammunition does the M16A2E3 use?

The M16A2E3 uses 5.56mm ammunition, which is standard for the M16 series of rifles. This caliber is designed for high-velocity, lightweight rounds that offer low recoil and high accuracy, making it suitable for various combat scenarios. The design of the 5.56mm round allows for effective engagement of targets at a distance while ensuring manageable firing characteristics for the user. This ammunition choice is integral to the rifle's performance, contributing to its reputation as a reliable and versatile weapon in military operations.

Other calibers listed, such as 7.62mm, 9mm, and 6.5mm, do not match the specifications of the M16A2E3 and are used for different types of firearms, further solidifying why 5.56mm is the correct answer.