What caliber is the M4 rifle?

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

Answer: (C)

The M4 fires a 5.56 mm cartridge. It’s part of the AR-15/M16 family and is chambered for the 5.56×45mm NATO round, a lightweight, high-velocity rifle cartridge standardized among NATO forces. This is what makes that specific caliber the M4’s designation. In contrast, 9 mm is a pistol round, 7.62 mm is a larger rifle round used by other platforms, and .50 BMG is a heavy anti-material round used in different weapon systems. The 5.56 mm choice supports a light, controllable recoil and the ability to carry more rounds in a magazine, which fits the M4’s role as a compact, infantry carbine.