jams. Later, they were made of sheet metal and, nowadays, of composite.

Between 1967 and 1970, the M16A1 was equipped with a chrome-plated barrel and slide for easier maintenance. Cleaning kits were distributed, and the weapon was even modified to allow the kit to be stored in its stock. The M16 was also equipped with 30-round magazines, like the AK-47.

M16A2 handled by a G.I. of the 25th Infantry Division during live-fire training in Hawaii.

 In the late 1970s, FN Herstal proposed an improved version of the 5.56 NATO round for the FN Minimi light machine gun, designated the SS109 (adopted as the M855 in the US Army), which is now the NATO standard. In 1981, Colt introduced a rifle adapted to the SS109 and featuring a heavier barrel than the first version of the M16. The M16A1 was indeed a very light assault rifle compared to other existing models. At 3.6 kg loaded, it was 300 grams lighter than the opposing AKM, 400 grams lighter than the Austrian Army's Steyr AUG, and 700 grams lighter than the French FAMAS.  The M16A2, which weighs 4.47 kg loaded, or over 800 grams, demonstrates that this new version represents a more profound doctrinal change than simply adapting to a new caliber, favoring accuracy and practical range over the weapon's lightness.

The weapon was adopted by the Marines in 1983 under the designation "M16A2," whose magazine became NATO's STANAG standard. The U.S. Army adopted it in 1985. FN Herstal was awarded the M16 production contract in 1988.

Since the U.S. Navy was not interested in the M16A2's three-round burst system, it ordered a separate production run, retaining the M16A1's free-burst system.  This model was designated the M16A3 and produced exclusively by the US FNMI factory. These rifles were upgraded in the early 2000s to the M16A4 standard.

In 1997, the M16A4 standard was adopted. It is identical to the M16A2, except for the sights, which have a reduced profile and are mounted on a standard rail allowing it to be replaced by various scopes, such as an ACOG sight. The M16A4 also lost the M16A2's round forearm in favor of a four-rail Picatinny forearm, manufactured by Knight Armament Company, to allow the installation of popular US infantry accessories.

The M16A2 is now a weapon that has corrected its teething problems. It remains a classic design and has undergone numerous adaptations.  Lightweight and compact versions with a short barrel and telescopic stock, known as the M4, are used by special forces. There are also several precision versions equipped with a scope for medium-range precision shooting, the DMR MK12 Mod 0/1/H, and a version equipped with an M203 or M230 grenade launcher (a standard rifle equipped with a grenade launcher).

Over eight million of the various versions of the M16 have been produced to date.