M16A2 and M16A4: The OG Black Rifles

March 14, 2023Mac Caltrider

Aviation Boatswain’s Mate (Fuels) 2nd Class Torien Collins fires an M16 rifle during a small arms qualification on the flight deck of the amphibious transport dock ship USS Green Bay (LPD 20), Aug. 11, 2016. US Navy photo by Mass Communication Specialist 3rd Class Patrick Dionne.

The M16 will go down as one of the most important innovations in the history of human warfare. It is the most ubiquitous 5.56-caliber weapon in the world, with more than 8 million fielded to soldiers spanning six continents. As iconic weapons go, the air-cooled, gas-operated, magazine-fed assault rifle ranks somewhere between the samurai sword and John Rambo’s M-60. 

It’s the original “black rifle.” The Model T of tactical firearms. Anyone who has ever served in the United States military — shit, anyone who has watched an action movie in the last 50 years — could describe it from memory. With its 20-inch barrel, innovative mixture of plastic and metal parts, and prominent A-frame front sight assembly, there’s just no mistaking the M16.


A Marine with 1st Battalion, 6th Marines aims his M16A4 in Helmand Province, Afghanistan, July 1, 2008. US Marine Corps photo by Sgt. Randall Clinton.

The M16 has been a prominent fixture in major conflicts around the world since the 1960s. First fielded by US Army Special Forces in Vietnam, it replaced the heavier, wood-and-steel battle rifles of yore, and ultimately outshined the AK-47 to be widely recognized as the most reliable standard-issue service weapon for the modern battlefield. 

The M16A2 and M16A4 are the rifle’s most popular variants. Both were carried by American troops in Iraq and Afghanistan. Now, the M16 is being phased out and replaced by new weapons capable of firing more powerful and accurate ammunition. But having spent more than five decades at the top of the rifle food chain, the M16’s legacy will live on forever.

Related: Butter Butter Jam!’: Troops Loved, and Hated, the M249 SAW

Origins of the M16 Variants

The M16’s ascent to becoming a staple of the American war machine got off to a rocky start. Like anything new to the military, the weapon was received with mixed emotions when it was first placed in the hands of GIs in 1963. 

Initially, there were widespread — and certainly valid — concerns that the M16 wasn’t rugged enough for the jungles and rice paddies of Vietnam. With its lightweight plastic handguards and pistol grip, smaller caliber bullets, and over-powdered cartridges, the M16 lacked the same heft as the wood-and-steel M14 it was replacing.

m16 Gulf War

A paratrooper with the 101st Airborne Division during a training exercise in Saudi Arabia, prior to the launch of operations in Kuwait, 1991. Photo courtesy of Wikimedia Commons.

Soldiers used to carrying the M14 (essentially an upgraded M1 Garand) were especially distrustful of the new, largely plastic rifle. Their misgivings were not unjustified. The M16’s flat receiver made it easy to accidentally press the magazine release button, and its non-crimped cam pin allowed the bolt to be inadvertently inserted backward. 

Once those issues were addressed, however, and an improved version of the rifle was rolled out, it became clear that the M16 was indeed the superior weapon platform. By 1967 — the year the number of American troops in Vietnam transcended the 500,000 threshold — the M16A1 was making its way to the battlefields of Indochina.

Related: Death From Afar: How the M40 Earned Its Place Among the Best Sniper Rifles

The M16A2 Sees Action Around the World 

While the M16A1 addressed the original design flaws and won over the rifle's loudest critics, there was still room for improvement. 

In 1979, the United States Marine Corps requested an updated model of the M16 that addressed the problem of the A1’s “pencil” barrel tending to overheat. The Corps also complained that the A1’s three-pronged “duckbill” flash suppressor kicked up excessive dirt when fired in the prone position. Their complaints were heard and the M16A2 was developed accordingly.


A soldier with US Army Alaska fires his M16 rifle during the USARAK Small Arms Competition on Joint Base Elmendorf-Richardson, Alaska, Nov. 18, 2014. US Army photo by Sgt. Brian Ragin.

The M16A2 replaced the original muzzle device with a “birdcage” compensator. The compensator’s closed bottom eliminated the issue of excessive dirt when shooting in the prone position and also helped further reduce muzzle climb while still diminishing flash. Additionally, the segment of the barrel that protrudes beyond the front sight was thickened to counteract overheating, while the rest of the barrel remained skinny so that an M203 grenade launcher could still be attached in place of a handguard. 

Furthermore, the barrel’s rifling was adjusted to a 1:7 twist rate, which helped stabilize the 5.56x45mm NATO standard ammunition that the M16A2 fired. A fully adjustable rear sight and a spent casing deflector were also added. The buttstock was strengthened, and rounded handguards replaced the solid, triangular handguards of the A1. 

Perhaps the most significant change was the selector switch. While the original M16 and the M16A1 were capable of semi-automatic and fully automatic fire, the M16A2 replaced the fully automatic firing mode with three-round burst. The US Army found that when inexperienced troops were under fire, they tended to set their rifle to fully automatic and waste precious ammunition. An M16A3 — essentially an A2 capable of being fired on fully automatic — was developed by the US Navy in smaller numbers for Navy SEALs and Seabees.


United States Marines carrying M16A4 rifles with fixed OKC-3S bayonets in Fallujah, Iraq, November 2004. Photo courtesy of Wikimedia Commons.

In 1983, the M16A2 became the standard-issue rifle for Marines. Three years later, the US Army followed suit. American troops carried the A2 into combat in places like Grenada, Panama, Somalia, and Iraq. However, during the Global War on Terror, the US military recognized a need for a more versatile rifle, and thus the M16A4 was born.

Related: The M203 Grenade Launcher: Farewell to the Infantry’s “Little Friend”

The Best M16 Ever Built

As the wars in Iraq and Afghanistan got underway in the early 2000s, it became apparent that deployed troops needed a more technologically advanced rifle, a weapon platform that could seamlessly incorporate the latest and greatest optics, lights, and lasers. 

Although first introduced in 1998, Marines put the new M16A4 through the crucible of combat during the 2003 invasion of Iraq. The new model replaced the A2’s fixed carry-handle iron sights with a flat-top Picatinny rail affixed to the upper receiver, which allowed for the attachment of either a carry-handle sight or a glass optic. The A2’s plastic handguards were also swapped out for a Knight’s Armament quad rail to accommodate additional components intended to improve the rifle’s lethality.

M16A4 Helmand

Marines with 1st Battalion, 6th Marines in Garmsir, Afghanistan, June 30, 2008. US Marine Corps photo by Cpl. Andrew Carlson.

By making the rifle more receptive to modifications without abandoning the M16’s proven design, the US military succeeded in creating a weapon that could be deadly accurate even in the hands of novice shooters.

In 2004, during the fight for Fallujah, the Marines’ optic-equipped M16s resulted in so many headshots that some observers initially thought that insurgents in the city had been systematically executed at point-blank range. 

“It’s incredibly easy to teach inexperienced shooters how to use the M16A4 to deadly effect,” said John Maxwell, a former Marine combat marksmanship instructor. “It takes under 30 seconds to explain basic functionality, and less than an hour to explain proper care, malfunction remediation, and marksmanship fundamentals. After one hour of instruction, an attentive person can learn to consistently hit targets at 300 meters.”

The M16A4 saw extensive use throughout two decades of conflict in Iraq and Afghanistan. However, the smaller derivative design — the M4 carbine, which had been improving alongside the M16 since its first iteration, the CAR-15, in 1965 — eventually became the preferred rifle to many troops. At less than 30 inches in total length, compared to the M16A4’s 40-inch design, the smaller, more manageable M4 proved to be better suited for vehicle operations and close-quarters combat. In 2005, the Army opted to equip forward-deployed soldiers with M4s instead of M16A4s.

M16 Seabee

A Seabee helps set a security perimeter at a project site near Fallujah, Iraq. US Navy photo by Photographer's Mate 2nd Class Eric Powell.

In 2014, in order to shorten the M16’s overall length without having to retire its massive inventory of rifles, the Marine Corps began to replace the A4’s bulky, fixed stock with collapsible stocks like those on the M4. This allowed smaller shooters to more comfortably maintain a proper firing position while wearing body armor. One year later, M4s were approved to replace M16A4s as the standard-issue rifle for Marine infantry units, relegating the M16A4s to support personnel.

Related: SIG Sauer Will Make the Army’s Next Generation Squad Weapon — Here’s What We Know

The End of an Era

Today, the M16A4 is more or less a relic in the US military. While the M4, MK12, and other similar weapons are still fielded, the Army is now in the process of switching from the M4 to the SIG Sauer XM5. And while the Corps was the first branch to request an improved rifle but the last to let the M16 go, even Marines are now being issued the M27 Infantry Automatic Rifle. 

While the M16 rifle is virtually extinct as far as the Pentagon is concerned, it's becoming more and more popular with gun collectors. Perhaps the growing appetite for “retro” rifles outfitted with things like carry-handle sights and 20-inch barrels will give the M16 a second wind in the civilian market. But even if this isn’t the end for the original black rifle, its era is over. The mission it was developed for has been fulfilled.

Read Next: Whistling Death: How the F4U Corsair Changed American Aviation

Mac Caltrider
Mac Caltrider

Mac Caltrider is a senior staff writer for Coffee or Die Magazine. He served in the US Marine Corps and is a former police officer. Caltrider earned his bachelor’s degree in history and now reads anything he can get his hands on. He is also the creator of Pipes & Pages, a site intended to increase readership among enlisted troops. Caltrider spends most of his time reading, writing, and waging a one-man war against premature hair loss.

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