Final answer:
The M16A2E3 uses 5.56×45mm NATO cartridges, which balances range and stopping power.
Step-by-step explanation:
The M16A2E3 is a variant of the M16 rifle used by the U.S. military. It is designed to fire the 5.56×45mm NATO cartridge. This rifle was developed to address the requirements of modern combat, and the ammunition size is a critical aspect of its design and capabilities. The 5.56mm caliber provides a good balance between range and stopping power, which has made it a standard for NATO forces.