The rifle grew out of a direct USMC request to Colt's Manufacturing Company in January 1980. Marine testers wanted a rifle that would survive rough handling better than the M16A1, reach out to longer ranges with the new NATO-standard cartridge, and stop burning through magazines on full-automatic.¹ The result, initially built and tested as the M16A1E1 through 1981, was accepted by the Marine Corps and then the Army as the M16A2, becoming the official USMC rifle in 1983.¹ Both the Army and the Marine Corps eventually fielded it, and it went on to arm a long list of allied militaries in Latin America, the Middle East and Southeast Asia over the following two decades, several of which still carry it today.

The Heavy Barrel and the Move to SS109/M855

{{photo-req side=right q="M16A2 rifle heavy barrel front sight close up" caption="The M16A2's thickened barrel profile forward of the front sight, adopted to resist bending under field handling." alt="Close-up of an M16A2 rifle barrel and front sight assembly"}}

The single biggest physical change from the M16A1 is the barrel. The M16A2 uses a heavier profile forward of the front sight base, thick enough to resist bending under rough handling by a factor Colt's own testing put at roughly nine times the M16A1's resistance, while the section under the handguards stayed slim so the weapon would not gain excessive weight.³ The barrel is also rifled at 1 turn in 7 inches (1:7) instead of the M16A1's 1:12, a twist rate fast enough to stabilize the longer, 62-grain SS109 projectile (adopted by the U.S. as M855) as well as the even longer L110 tracer round used alongside it.⁴ NATO had standardized the SS109 cartridge on 28 October 1980, originally developed for the FN Minimi light machine gun and the FN FNC, giving the alliance a common 5.56mm loading with a steel-cored bullet that penetrated better against helmets and light armor at range than the older 55-grain M193.⁴ The heavier bullet actually lowered muzzle velocity slightly, from about 994 m/s with M193 in the M16A1 to roughly 948 m/s with M855 out of the M16A2's 508 mm (20 inch) barrel, a trade Army testers judged worthwhile for the improved long-range performance and standardization with NATO allies.⁵

Sights, Stock and the Fire Control Group

The M16A1's simple flip-type aperture, which merely toggled between a close and long-range setting, was replaced on the M16A2 by a fully adjustable rear sight with click adjustments for both windage and elevation covering 300 to 800 meters, borrowed conceptually from target-shooting rifles.⁶ The front sight post also changed from a round post with five elevation settings to a flat-faced post with four, correcting a light-refraction issue that had thrown some M16A1 groups off center.⁶ The buttstock, pistol grip and handguards were remade in a tougher glass-filled Zytel polymer, the stock was lengthened about 5/8 of an inch (0.62 in / 15.7 mm), and the buttplate gained a coarser, non-slip texture, changes aimed squarely at Marine complaints that the M16A1 felt fragile and slipped on the shoulder during firing.⁶ None of this altered the basic operating principle. The M16A2 still cycles by direct gas impingement, locks with a rotating bolt, and feeds from STANAG detachable magazines of 30 rounds, retains iron sights, a bayonet lug and grenade-launching capability with the M203 under-barrel launcher.

Trading Full-Auto for a Three-Round Burst

{{photo-req side=left q="Eugene Stoner AR-15 designer portrait" caption="Eugene Stoner, the original designer of the AR-15/M16, publicly disagreed with several changes the Marine Corps made in developing the M16A2." alt="Portrait of Eugene Stoner, firearms designer"}}

The most contested change was the fire control group. The M16A2 dropped the M16A1's full-automatic setting in favor of a mechanical three-round burst limiter, selectable alongside safe and semi-automatic. The Marine Corps wanted the change to conserve ammunition and reduce the tendency of green troops to empty a magazine in one long automatic burst. U.S. Army analysts separately concluded three-round groups offered the best balance of ammunition economy, accuracy and firepower.¹ The change was not universally welcomed. ArmaLite's original AR-15/M16 designer Eugene Stoner argued publicly that his own testing had already shown three rounds was, if anything, the worst possible burst length, reasoning that it gave a rifleman the least margin for recoil control while still capping his firepower against an opponent's full-automatic AK-pattern rifle.⁸ Stoner also disliked the sight change, telling historian Edward Ezell that Marine target shooters had turned a combat rifle into something closer to a target rifle.⁸

Development ran through 1980-1982 as a joint USMC-Colt program. Testing at the Naval Surface Warfare Center in Dahlgren, Virginia in August 1980 recommended the heavier barrel profile, and Marine Corps trials of developmental M16A1E1 rifles that November and December convinced testers the package was ready.¹ Type classification as the M16A2 followed in September 1982, and the U.S. Marine Corps made it the standard infantry rifle in 1983, well ahead of the Army's own transition.¹

Colt could not keep the contract to itself for long. In 1988, with Colt's Hartford workforce on strike, FN Herstal's American subsidiary, FN Manufacturing, won a U.S. government solicitation to build M16A2 rifles at a plant in Columbia, South Carolina, bidding $420 per rifle against Colt's $477.50 and taking a $112.1 million, five-year contract for 266,961 rifles.⁹ From that point the U.S. government effectively dual-sourced its M16A2 production between Colt's Manufacturing Company and FN, a pattern that carried forward into M16A4 and M4 production in the following decades.

The rifle's cultural profile grew alongside its combat record. It is the weapon most associated on screen with the 1993 Mogadishu raid through Ridley Scott's 2001 film Black Hawk Down, and it has been a playable weapon in tactical shooters since the late 1990s, appearing in Red Storm Entertainment's original Tom Clancy's Rainbow Six in 1998 and later in Battlefield 2 in 2005, among many other titles.¹¹

{{photo-req side=left q="US Marine M16A2 rifle Gulf War 1991 Desert Storm" caption="A U.S. Marine with an M16A2 during Operation Desert Storm, 1991." alt="US Marine holding an M16A2 rifle during the Gulf War"}}

The M16A2 was the rifle American ground troops carried into the Gulf War in 1991, and it remained the Army's primary infantry rifle through most of the 1990s even as the shorter M4 carbine began appearing with special operations and some conventional units. The Marine Corps stuck with the full-length M16 pattern longer, moving to the visually similar M16A4 starting in 1997 rather than jumping straight to the M4.¹⁰ By around 2005 the M4 had displaced the M16A2 as the primary weapon of forward-deployed U.S. Army soldiers, and the Army formally began replacing the M16 as its primary infantry rifle in front-line combat units starting in 2010, though M16-pattern rifles stayed in wide use with support troops, National Guard units and training commands for years afterward.¹⁰

The M16A2 armed the bulk of U.S. ground forces during the 1991 Gulf War, where it performed largely without the sand-related jamming problems that had dogged earlier M16 variants in Vietnam, thanks to decades of ammunition, chrome-lined chamber and maintenance improvements.¹ It was still the standard-issue Army and Ranger rifle two years later during the October 1993 Operation Gothic Serpent raid in Mogadishu, Somalia, the battle depicted in Black Hawk Down.¹¹

{{photo-req side=right q="US Army Rangers Mogadishu 1993 Somalia street" caption="U.S. Army Rangers in Mogadishu during Operation Gothic Serpent, October 1993." alt="US Army Rangers on a street in Mogadishu, Somalia, 1993"}}

Rangers and Delta Force operators involved in the raid, including Task Force Ranger personnel such as Staff Sergeant Matt Eversmann's chalk, carried M16A2s and the newer M4 carbine side by side.¹¹ The battle became a widely cited case study in 5.56mm terminal performance criticism. In the close, urban fighting around the crash sites, the SS109/M855 round sometimes failed to reliably incapacitate Somali fighters with hits that were not immediately vital, and the fine sand endemic to Mogadishu was blamed for a number of weapon stoppages during the sustained firefight.¹¹

{{photo-req side=left q="Mogadishu Somalia city map Horn of Africa" caption="Mogadishu, Somalia, site of the October 1993 battle that became a defining case study in M16A2 combat performance." alt="Map of Mogadishu and the Horn of Africa region"}}

The M16A2 also equipped U.S. and allied forces during the opening years of the Iraq War following the 2003 invasion, though by then the M4 carbine was already displacing it in front-line infantry and mechanized units for its shorter length inside vehicles and buildings.¹⁰

No further factory-designated M16A2.x sub-variants exist in U.S. service records. The direct institutional successor is the M16A3, essentially an M16A2 with the removable carry handle and flat-top Picatinny rail receiver, adopted in small numbers mainly by the U.S. Navy and Air Force security forces for optics compatibility.¹² The more widely fielded successor is the M16A4, which paired the M16A2's fire control group and heavy barrel with the flat-top receiver as the U.S. Marine Corps' standard rifle from 1997 until the Corps' own switch to the M4 carbine began in 2015-2016.¹⁰

{{photo-req side=right q="M16A4 rifle flat top rail Marine Corps" caption="The M16A4, the U.S. Marine Corps' flat-top successor to the M16A2, kept the same heavy barrel and fire control group." alt="M16A4 rifle with flat-top Picatinny rail receiver"}}

Commercially, Colt sold the semi-automatic-only civilian Colt AR-15A2 built on the same profile for the sporting market, and the M16A2's heavy-barrel, 1:7-twist barrel profile was later carried directly into the original M4 carbine, which is best understood as a shortened M16A2 rather than a clean-sheet design.¹³

The United States remains the largest historical operator, having fielded the M16A2 across the Army, Marine Corps, Air Force and Navy from the 1980s through the 2010s, with substantial numbers still in reserve, training and support-unit inventories.¹ A long list of U.S. security partners received or still operate the M16A2 through Foreign Military Sales and surplus transfers, including Chile, Peru, Mexico, Colombia, Ecuador, Guatemala, Honduras, the Dominican Republic, El Salvador, Costa Rica and Panama across Latin America, plus Jordan, Lebanon, Malaysia, Thailand, Singapore and the Philippines in the Middle East and Southeast Asia.² Iraq's post-2003 security forces also received M16A2s as part of broader U.S. rebuilding efforts, and Argentina and Brazil both operated the type in earlier decades before retiring it in favor of domestic or other foreign designs.² Some of these countries, notably the Philippines through the Elisco Tool Manufacturing joint venture with Colt, had already built earlier M16A1-pattern rifles under license locally before receiving M16A2-standard rifles and kits through government-to-government channels.¹⁴

{{photo-req side=left q="Philippine Army soldier M16 rifle training" caption="A Philippine Army soldier training with an M16-pattern rifle, a type long supplied and locally assembled under license from Colt." alt="Philippine Army soldier with an M16 rifle"}}

Most of these operators acquired their M16A2 stocks either as direct government surplus transfers once the U.S. Army and Marine Corps began shifting to the M4 carbine and M16A4, or through standard Foreign Military Sales channels during the 1990s and 2000s, when the M16A2 was still in full-rate American production. A handful, like Mexico and Colombia, use the rifle heavily in internal security and counter-narcotics operations rather than conventional warfighting, which has kept demand for spare parts and armorer support high for a design otherwise phased out of frontline U.S. service.²

The M16A2's clearest rival for most of its service life was not a foreign design but its own shortened descendant, the M4 carbine. Both share the same 5.56x45mm NATO chambering, the same 1:7 heavy-barrel philosophy, and largely the same fire control internals, but the M4's 368 mm (14.5 in) barrel trades muzzle velocity and long-range accuracy for a package roughly 8 inches shorter overall, a difference that mattered enormously once U.S. forces started fighting inside vehicles, buildings and helicopters in Iraq and Afghanistan rather than in the open terrain the M16A2 was optimized for.¹⁰ Set against a contemporary foreign design like the Steyr AUG, the comparison is about layout philosophy rather than caliber. The AUG's bullpup layout packs a full-length 508 mm barrel (nearly identical to the M16A2's) into a much shorter overall weapon by moving the action behind the trigger group, at the cost of ejecting hot brass close to a right-handed shooter's face and complicating quick side-switching, a trade the U.S. military never adopted despite evaluating bullpup designs repeatedly from the 1980s onward.

The M16A2's full-length barrel gives it a genuine edge in retained velocity and effective range over the M4 at distances past 300 meters, a fact that kept the related M16A4 in Marine Corps rifle-squad service years after the Army had already leaned into the M4 for close-quarters flexibility.¹⁰ Whether that range advantage still outweighs a carbine's handling in modern combined-arms fighting is precisely the argument that eventually pushed even the Marine Corps to switch by 2016.

What replaced the M16A2 in U.S. service? The U.S. Army largely replaced the M16A2 with the shorter M4 carbine by the mid-2000s, while the Marine Corps first moved to the M16A4 in 1997 and only began its own switch to the M4 carbine in 2015-2016.¹⁰

Is the M16A2 still in service anywhere? Yes. While U.S. front-line units have largely moved on to the M4 and M16A4, the M16A2 remains in active or reserve use with numerous allied militaries in Latin America, the Middle East and Southeast Asia, and with U.S. National Guard, training and support units.²

What caliber does the M16A2 fire? The M16A2 is chambered for 5.56x45mm NATO, firing the heavier 62-grain SS109/M855 cartridge through a 1:7 twist barrel, a change from the 55-grain M193 round used in the earlier M16A1.⁴

Why does the M16A2 not have a full-automatic setting? The U.S. Marine Corps specifically requested the three-round burst in place of full-automatic fire to conserve ammunition and improve controlled accuracy, though the change was privately criticized by AR-15/M16 designer Eugene Stoner as offering no real advantage over full-auto in a firefight.⁸

How much does an M16A2 cost? Government unit prices from the 1988 FN Manufacturing contract were about $420 per rifle. Later Foreign Military Sales and commercial-market prices for legally transferable examples have run into the thousands of dollars given the type's National Firearms Act restrictions in civilian hands.⁹