.223 / 5.56

.224 (.223 Remington / 5.56×45mm NATO)

History & Design Intent

The .224-inch bore family grew out of the late-1950s U.S. small-caliber, high-velocity program. Remington commercialized the .223 in 1964 and the military adopted the closely related 5.56×45mm NATO for the M16, trading the heavy .30-caliber battle rifle round for a lighter, flatter-shooting cartridge that let infantry carry far more ammunition.

Operational Profile

Light 55–77 grain bullets driven to roughly 2,700–3,200 fps give a flat trajectory and mild recoil. It is the dominant chambering of the AR-15 platform and is used everywhere from varmint hunting and 3-gun competition to police and military service rifles. (5.56 NATO is loaded hotter than commercial .223 — check the chamber before mixing them.)