The 5.56×45mm cartridges are the NATO standard ammunition primarily used in carbines, assault rifles and the M249 Squad Automatic Weapon. The first version of the round was developed from the older .222 Remington round in the late 1950's. Soon after, the AR-15 and the new bullet were adopted by the U.S. Army as the M16 and 5.56×45mm M193. In the early 1980's the bullet design was updated by Fabrique Nationale in order to improve the reliability and lethality of the M16. This resulted in the M16A2 and the 5.56x45mm NATO round.
The M855 Ball is used by the M249 machine gun and the M16A2/A3/A4 and M4-series weapons. The cartridge is intended for use against personnel and unarmored targets. It is a gilded metal-jacketed, lead alloy core bullet with a steel penetrator. The cartridge is identified by a green bullet tip.
The M856 Tracer is used by the M249 machine gun and the M16A2/A3/A4 and M4-series weapons. The tracer is intended to permit visible observation of the bullet's in-flight path to the point of impact by delivering a visible red light signature through its trajectory. It is ballistically matched to the M855 ball cartridge, but it does not have a steel penetrator. The cartridge is identified by an orange bullet tip.
The M995 AP is used by the M249 machine gun and the M16A2/A3/A4 and M4-series weapons against light armored targets. It offers the capability to defeat these targets at ranges 2 to 3 times that of currently available 5.56mm ammunition. The projectile consists of a dense metal penetrator (tungsten carbide), which is enclosed by a standard gilding metal jacket. This cartridge is identified by a black bullet tip.