What caliber do the M16A4 and M4 Carbine use?

• A. 5.56 mm
• B. 7.62 mm
• C. 9 mm
• D. .50 BMG

Answer: (A)

The rifles in question are chambered for the 5.56x45mm NATO cartridge. This lightweight, high-velocity round was adopted to give soldiers a controllable weapon with good magazine capacity, enabling effective fire while keeping ammunition weight reasonable. The M16A4 and M4 Carbine share this chambering, which is a defining feature of both platforms.

The other calibers correspond to different systems: 7.62 mm is the older, larger round used by rifles like the M14 and many machine guns; 9 mm is a pistol/submachine gun round; .50 BMG is a heavy, long-range round used by heavy machine guns and anti-material rifles.