M16 (rifle)

The M16 is an assault rifle adopted by the United States military from the late 1960s onwards. It fires a small, high-velocity round designated 5.56×45 mm. The rifle operates by gas: a portion of the gas produced by the fired round is redirected to cycle the bolt, allowing the weapon to chamber the next round.

The basic design derives from the AR-15, developed by Eugene Stoner and engineers at ArmaLite. The design rights were later sold to Colt, which produced the rifle for the U.S. military. Distinctive features include the use of lightweight metal and polymer for the handguard and stock, and the upper-mounted charging handle.

Operating mechanism

The M16 uses a magazine fed from below the rifle. Earlier versions carried 20 rounds; 30-round magazines later became standard. The selector switch offers three or two positions: safe, semi-automatic, and full-automatic or burst fire, depending on the variant. The rifle's rail system allows attachment of optical sights, scopes, and other accessories.

Variants

Major variants include the M16A1, which introduced improvements to reliability and ease of maintenance; the M16A2, featuring a heavier handguard, adjustable sights, and burst-fire capability; and the M16A4, equipped with a top rail and provisions for electronic attachments. Shortened variants of the same family include the CAR-15 and M4 carbine, suitable for close-quarters and confined-space operations.

Adoption and distribution

The M16 saw widespread service during the Vietnam War. Early adoption was hampered by reports that the rifle would jam if not cleaned regularly, issues attributed to the powder used, inadequate maintenance training, and incomplete finishing of internal components. Subsequent modifications reduced these problems. The rifle eventually became widely adopted by many nations and military forces, and the 5.56 mm round became standard among many military establishments.