5.56×45mm NATO is a small, high-velocity centerfire rifle cartridge widely used in AR-15-pattern rifles. It is closely related to, but not identical to, the .223 Remington.

5.56 NATO is a lightweight, flat-shooting intermediate rifle cartridge developed for military service and now common in civilian sporting rifles. It produces relatively light recoil for a centerfire rifle round, which makes it easy to shoot accurately and quickly. Ammunition is widely available and generally affordable. It is commonly used for target shooting, training, varmint and predator control, and home defense in carbine platforms. One important note: 5.56 NATO is loaded to higher pressure than .223 Remington — rifles chambered for 5.56 can typically fire both, while a .223-only chamber should not be fed 5.56, so the specific chamber marking on a given firearm is worth verifying.

General information about this caliber — not a recommendation for this specific firearm.