M16A4: The U.S. Marines Go-To Rifle Still Looks Unstoppable

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Key Points: The M16A4 rifle, an evolution of the original M16 designed by Eugene Stoner, served as the Marine Corps’ primary weapon from 1997 until 2015, when it was replaced by the M4 Carbine.

-Featuring a flat-top receiver, MIL-STD-1913 rail, and the ability to mount grenade launchers and optics, the M16A4 was effective but became increasingly outdated for close-quarters combat in Iraq and Afghanistan.

-Marines found the weapon too long and prone to jamming in dusty environments. Although the Marine Corps eventually switched to the M4, the delay in modernization highlighted systemic issues in equipping troops with the best tools for combat.

M16A4, The Marine Corps Primary Weapon

Eugene Stoner, an engineer for ArmaLite Corp., developed the AR15 rifle in the late 1950s. Armalite got favorable reviews but didn’t get anywhere with selling it to the government. 

The rifle replaced the M14’s wooden stocks with black plastic, and the caliber was changed to .223/5.56mm. 

In 1959, Colt obtained a license for the design and sold it to the US Air Force in 1962. The Department of Defense redesignated the rifle, the M16, and since then, the upgraded and variant models of the M16 have served in the US military.

Early Issues And Changes

Early models of the M16 were used in Vietnam during the mid-1960s but were prone to jamming. Most of the issues were ironed out with better training on cleaning the weapon, changing the powder in the ammunition used, and developing the forward assist, reducing malfunctions. This weapon was called the M16A1.

The rifle was used throughout the US military until the early 1980s when the military changed the design to using a heavier barrel for longer sustained fire. Also, the fully automatic feature was removed as it was considered wasteful of ammunition and inaccurate.

Instead, the rifle incorporated the three-round burst. This model was dubbed the M16A2. 

The M16A4 and the M4 Carbine were first issued to select units in the mid-90s. In Special Forces, we were issued M4s in about 1995. The Marine Corps adopted the M16A4 in 1997. It was the primary weapon of Marines until 2015 when the Corps announced that it was switching to the M4. 

The M16A4 Characteristics

The Marine Corps has characterized the M16A4 Service rifle and the M4 Service Carbine as 5.56mm, magazine-fed, gas-operated, air-cooled, shoulder-fired weapons that can be fired either in automatic three-round bursts or semiautomatic single shots, as determined by the position of the selector lever.

The fourth-generation M16A4 is essentially an M16A2 but with a flat-top receiver, a MIL-STD-1913 rail, and a handguard. It also has an optional M5 Adapter Rail System for mounting a range of accessories. The system can accommodate modern optics and accessories and incorporate both the M203 and M320 40mm Grenade Launchers.

M16A4 Specs 

Caliber: 5.56mm

Magazine Capacity: 30 rounds

Weight: 9.87 pounds (with the sling and loaded mag)

Length: 39.6 inches

Barrel length: 20 inches

Range: 550 meters (point target); 800 meters (area)

Maximum Sustained Rates of Fire:

Semiautomatic: 45 RPM

Burst: 90 RPM

Sustained Rate of Fire: 12-15 RPM

Why Did the Marine Corps Wait So Long?

The Marine Corps published a video for recruits explaining all parts of the M16A4. The Marines continued to use it in Iraq and Afghanistan for years despite the fact that the weapon was outdated and prone to jamming in each location’s dusty environs. 

The Army had used the M4 carbine for about 15 years before the Marine Corps switched over. 

However, the M16A4 is still used by support or non-infantry Marines. Marine Corps Commandant Gen. Robert Neller approved the switch, listening to his Marines, who had complained that after years of close-quarters battle, vehicle-borne operations, and urban combat, the M16A4 was too long and unwieldy for those such operations. 

The long wait to switch is an example of service chiefs waiting too long to change issues that could save troop lives. In this case, it happened to be the Marines; however, the process for all of the armed services should be quicker. 

The service chiefs are the leaders who must take care of the troops doing the fighting. And they deserve the best. 

About the Author: 

Steve Balestrieri is a 19FortyFive National Security Columnist. He served as a US Army Special Forces NCO and Warrant Officer. In addition to writing for 1945, he covers the NFL for PatsFans.com and is a member of the Pro Football Writers of America (PFWA). His work was regularly featured in other military publications.