M14 rifle in the context of "M1 Garand"

The M16 rifle (officially designated Rifle, Caliber 5.56 mm, M16) is a family of assault rifles adapted from the ArmaLite AR-15 rifle for the United States military. The original M16 rifle was a 5.56×45mm automatic rifle with a 20-round magazine.

In 1964, the XM16E1 entered US military service as the M16 and in the following year was deployed for jungle warfare operations during the Vietnam War. In 1969, the M16A1 replaced the M14 rifle to become the US military's standard service rifle. The M16A1 incorporated numerous modifications including a bolt-assist ("forward-assist"), chrome-plated bore, protective reinforcement around the magazine release, and revised flash hider.

The 7.62×51mm NATO (official NATO nomenclature 7.62 NATO) is a rimless, bottlenecked, centerfire rifle cartridge. It is a standard for small arms among NATO countries.

First developed in the 1940s, the cartridge had first been introduced in U.S. service in 1954 for the M14 rifle and M60 machine gun.

An AR-15–style rifle is a lightweight semi-automatic rifle based on or similar to the Colt AR-15 design. The Colt model removed the selective fire feature of its predecessor, the original ArmaLite AR-15, which is a scaled-down derivative of the AR-10 design (by Eugene Stoner). It is closely related to the military M16 rifle.

ArmaLite sold the patent and trademarks for both to Colt's Manufacturing Company in 1959 after the military rejected the design in favor of the M14. After most of the patents for the Colt AR-15 expired in 1977, many firearm manufacturers began to produce copies of the rifle under various names. While the patents are expired, Colt has retained the trademark to the AR-15 name and is the sole manufacturer able to label their firearms as such.