M16 information

The M16 entered United States Army service as the M16A1 and was deployed for jungle warfare in the Republic of South Vietnam in 1963, becoming the standard US Rifle of the Vietnam War by 1969; replacing the M14 Rifle in that role. The US Army retained the M14 in CONUS, Europe, and South Korea until 1970. Since the Vietnam War, the M16 rifle family has been the primary infantry rifle of the U.S. military. With its variants, it has been in use by 15 NATO countries, and is the most produced firearm in its caliber.

Variant originally adopted by the U.S. Air Force. This was the first M16 adopted operationally. This variant had triangular handguards, a three-pronged flash suppressor, and no forward assist. Bolt carriers were originally chrome plated and slick-sided, lacking forward assist notches. Later, the chrome plated carriers were dropped in favor of Army issued notched and parkerized carriers though the interior portion of the bolt carrier is still chrome-lined. The Air Force continues to operate these weapons and upgrades them as parts wear or break and through attrition.

The U.S. Army XM16E1 was essentially the same weapon as the M16 with the addition of a forward assist and corresponding notches in the bolt carrier. The M16A1 was the finalized production model in 1967. To address issues raised by the XM16E1's testing cycle, a closed, bird-cage flash suppressor replaced the XM16E1's three-pronged flash suppressor which caught on twigs and leaves. Various other changes were made after numerous problems in the field. Cleaning kits were developed and issued while barrels with chrome-plated chambers and later fully-lined bores were introduced.

With these and other changes, the malfunction rate slowly declined and new soldiers were generally unfamiliar with early problems. A rib was built into the side of the receiver on the XM16E1 to help prevent accidentally pressing the magazine release button while closing the ejection port cover. This rib was later extended on production M16A1s to help in preventing the magazine release from inadvertently being pressed. The bolt cam pin and the hole it rides in the bolt were tapered to prevent the bolt from being inserted upside down (creating a failure to fire). The M16A1 remains in service in limited numbers in the United States but is still standard issue in many world armies.