Perhaps one of the most iconic military cartridges, the 5.56x45mm NATO ammunition, commonly referred to as the 5.56 NATO, has been in active use in the United States Armed Forces since 1964.
5.56×45 NATO ammo features a rimless and tapered bottleneck case that measures 44.70mm (1.76 inches) in length and ranges from a 6.43mm diameter at its neck to a 9.58mm diameter at its base. This casing houses a boat-tailed bullet with a diameter of 5.70mm, or .224 inch. With both bullet and shell, the 5.56 cartridge reaches 57.40mm (2.26 inch) in length.
While the original 5.56x45mm bullet was 55 grain (gr) of lead, the standard bullet now weighs 62 gr and consists of a lead base topped with a steel penetrator. The added weight increases the ammunition’s penetration and velocity, improving its performance.