Marines New Assault Rifle

The Marines Are Fielding a New Assault Rifle

The M27 Infantry Automatic Rifle is going to all combat grunts.

By Kyle Mizokami

U.S. MARINE CORPS PHOTO BY LANCE CPL. JON SOSNER

The U.S. Marine Corps is expanding its use of a new automatic rifle, issuing it to all Marine infantry and other Marines at the very tip of the spear. The M27 Infantry Automatic Rifle will replace the M4 carbine in many combat-related positions. Other troops will continue to use the M4.


The Marine Corps adopted the M27 Infantry Automatic Rifle in 2010 to replace the M249 Squad Automatic Weapon. The Marines valued the M27’s ability to fire short, accurate bursts of suppressive fire at longer distances and issued the firearm to one Marine per infantry fire team, or three per squad. The fast-firing, high-capacity (though less accurate) M249 remains in Marine Corps service and can still be issued as needed.

Now the Marine Corps has decided that the M27 is sufficiently better than the M4 carbine to warrant forking over the $3,000 cost for almost all frontline Marines. According to a Military.com interview with Commandant of the Marine Corps General Robert Neller, the Corps will issue every Marine in an infantry squad the M27. Neller also identified “forward observers, fire support teams, and engineers” as good candidates for the weapon, but said that mortarmen and Javelin anti-tank missile operators would probably keep the M4 for now.

The M27 IAR is a Heckler and Koch 416 assault rifle that, although outwardly similar to the M4 carbine, uses a piston operating system instead of the M4 carbine’s gas impingement system to drive the bolt. The result is a cooler, cleaner rifle that recycles hot gunpowder gases into the carbine’s action to cycle the bolt.

More importantly, the M27 is a more accurate weapon. The M27’s rifle barrel is slightly longer and thicker than the M4’s, giving the M27 a slight range advantage and making it less prone to overheating. The barrel is free-floated, meaning it makes contact with the rest of the rifle only at the receiver, which prevents accuracy degradation when the barrel warms after repeated firing.

A number of standard accessories round out the M27, the most important being a Trijicon ACOG Squad Day Optic, with 3.5x magnification and Harris folding bipod. The result is a stable shooting platform that allows target identification and precision fire out to distances of up to 600 yards, at least 100 yards farther than the M4. The ACOG also incorporates a rugged miniaturized reflex sight for close quarters shooting.

The M27 and M4, although different internally are still relatively simple to operate and use the same ammunition, meaning keeping two types of rifles running in wartime won’t be as much of a problem as it sounds. The M27 should make Marine Corps infantry units more accurate while using fewer rounds to service a target.