A Marine with the M27. photo from military.com.

The gun the United States Marine Corps has been looking to as a replacement for its squad-level light machine gun, the M249 SAW, may become the new USMC service rifle.

According to military.com, the Marine Corps’ experimental battalion, the California-based 3rd Battalion 5th Marines, has been conducting pre-deployment exercises with the M27 Infantry Automatic Rifle (IAR) “to evaluate it as the new service rifle for infantry battalions,” the story reports. The move comes after the recent decision to switch Marine infantry battalions’ primary weapon from the M16A4 rifle to the M4 carbine..

The story says the battalion is set to deploy aboard the 31st Marine Expeditionary Unit this spring. As a part of its workup and deployment, the unit has been charged with testing and evaluating a host of technologies and concepts, ranging from teaming operations with unmanned systems and robotics to experiments with differently sized squads.

“When they take the IAR and they’re training out there with all the ranges we do with the M4, they’re going to look at the tactics of it. They’ll look at the firepower, and they’ll do every bit of training, and then they’ll deploy with that weapon, and we’ll take the feedback to the Marine Corps to judge,” said 1st Marine Division, Maj. Gen. Daniel O’Donohue in the story.

So what’s the difference from the M27 and the M16A4 the Corps sent by the wayside?

The biggest difference, from an operational perspective, is the fire selector. The M4 can be set to semi-auto or 3-round burst, whereas the M27 can fire in semi-auto or full-auto modes, allowing it to serve a role similar to a light machine gun while retaining the accuracy and range of a rifle. Opponents of using the M27 as a primary service rifle worry users will blow through ammo too quickly like they did with earlier iterations of the M16, resulting in the three-round burst setting on the M16A4 and M4.

At its core, the M27 is the Heckler & Koch HK416, and has been replacing a portion of the belt-fed M249 SAW light machine guns currently used by automatic riflemen in Infantry and Light Armored Reconnaissance Battalions since about 2013.

The program to develop and issue an IAR has been in the works since about 2000. It was given official program status in 2005 and began in July, when the USMC sought information from gun makers.

The objectives of the IAR were portability and maneuverability, reduction of visual identification of an automatic weapon to the enemy, strengthening the gunner’s participation in counter-insurgency situations, and maintaining a high volume of fire. An initial requirement for a 100-round capacity magazine was dropped in favor of the standard 30-round STANAG magazine, meaning it fires 5.56x45mm, non-linked ammunition, like the M4.

The H&K model beat out three other finalists in December 2009 and was designated the M27 in 2010. The designation was named after the 2nd Battalion 7th Marines who had been testing the rifle prior to September 11, 2001.

Marines Testing AR-Style Automatic Rifle
A Marine with the M27 IAR. photo from wikipedia. web photo

In 2001, Gen. James Amos approved the termination of a Limited User Evaluation and the replacement of the M249, and several thousand have been issue to Marines in the years since in the Afghanistan Theater.

The M27, being an AR-platform rifle, is lighter and handier than the bulky and heavy M249, and it doesn’t require special gear to carry large magazines of belt-fed ammo. It’s also more accurate than the M249 and can hit targets at long distances when switched to semi-auto mode. Its functionality has allowed it to be used in the Designated Marksman Role, a task the M249, a machine gun designed mostly for suppression fire, can’t perform.

To make up for the difference in ammo count between the M249 and the M27, the magazine supply is spread out among the members of a squad over as many as 22 30-round magazines, totaling about 600 rounds, or the typical ammo load of the M249. If necessary, Marines carrying extra ammo for the M27 can use those magazines in their own M4. Additionally, a rifleman normally carries seven 30-round magazines, whereas an IAR gunner carries up to 16 magazines and as many as 21.

When the M27 was being developed, high-capacity magazines were still unreliable, but they have come a long way since. The M27 has been successfully tested with the Armatac SAW-MAG 150-round drum magazine and other 50- to 100-round mags are being explored. The M27 is also the reason the Marine Corps has banned the use of the PMAG 30 Gen M2 magazines since 2012. The popular plastic mags will not work with the M27 because of the front plastic bevel on the PMAG. In response, Magpul tweaked its newer PMAG 30 GEN M3 magazines, which are compatible with the M16, M4, and M27.

The M27 features rail sections for installation of various accessories, such as optics and grips. A sort-stroke pistol operates a rotating bolt in the gas-operated action. The rifle features a free-floating barrel to aid in accuracy and a foldable bipod can be used to support the front section of the rifle when needed for fire suppression.

The overall length of the M27 is 37 inches, and its barrel measures 16.5 inches. The adjustable stock can reduce the length to a more manageable 33 inches, and the rifle weighs 8 pounds unloaded. Its rate of fire is about 700 to 850 rounds per minute, with an effective range of 550 meters and a suppressive range of about 3,600 meters. It features a flip-up rear rotary sight and a front post to back up any additional optics. But it’s still an HK416, not an M27, until it gets all the accessories the USMC requires.

The rifle is topped with a Trijicon ACOG Squad Day Optic, which is a 3.5X35 machine gun optic that has a Ruggedized Miniature Reflex sight affixed above for close-quarters engagements. The optic was created for the M249 and offers slightly less magnification but longer eye relief than the ACOG Rifle Combat Optic. It’s also issued with the Vickers Combat Applications sling and rail sling mounts, AIM Manta Rail Covers, Harris bipod, KAC backup irons, a foregrip, and bayonet lug.

To learn more about the history and details of the M27, go here.