The M27 Infantry Automatic Rifle (IAR) is a lightweight magazine-fed 5.56mm select-fire weapon based on the HK416 rifle designed and manufactured by the German company Heckler & Koch. It is used by the United States Marine Corps and is intended to enhance an automatic rifleman’s maneuverability. The U.S. Marine Corps initially planned to purchase 6,500 M27s to replace a portion of the M249 light machine guns employed by automatic riflemen within Infantry and Light Armored Reconnaissance Battalions. Approximately 8,000–10,000 M249s will remain in service with the Marine Corps to be used at the discretion of company commanders. In December 2017, the Marine Corps announced that it would equip every member of an infantry squad with the M27.
The M27 is based on the H&K HK416. It features a gas-operated short-stroke piston action with a rotating bolt and a free-floating barrel. The handguard has four MIL-STD-1913 Picatinny rails for use with accessories and optics. The simpler gas-piston rifle system reduces the amount of time it takes to resolve malfunctions on the IAR compared with the M249. Alternate calibers other than 5.56 mm are being considered for the M27.
The M27 IAR was adopted as the standard issue service rifle of the Marine Corps infantry – replacing the M4A1 – in 2018. Once the change is fully implemented, the M27 IAR will be issued to all riflemen in the Marine Corps infantry, while the M4A1 will only be issued to non-infantry Marines.
The M27 IAR was originally fielded as a proposed replacement for the M249 SAW between the years 2010 and 2017. During that time period, it was distributed one per four-man fireteam, three per squad, 28 per company, 84 per infantry battalion and 72 per Light Armored Reconnaissance Battalion, with a total of 4,476 being serviced by the Marine Corps as a whole. However, the M249 was not completely replaced by the M27 IAR, and six M249s were still issued to rifle companies between 2010 and 2017.
The M27 usually draws ammunition from a standard 30-round STANAG magazine. The improved STANAG magazine with the tan-colored anti-tilt follower is favored over the previous version with the green follower because it can be inserted more easily and the anti-tilt follower can handle high rates of fully automatic fire with less chance of malfunction. There have been issues with some STANAG magazines sticking in the magwell, especially when painted and or damaged. While a rifleman normally carries seven 30-round magazines, an IAR gunner has to carry up to sixteen, and may carry as many as twenty one, due to its role and fully automatic rate of fire. The magazine well has a flared opening that aids in magazine insertion, but a PMAG 30 GEN M2 magazine cannot be inserted due to the frontal plastic bevel on the PMAG. Because the M27 cannot be fed from the widely used M2 PMAG magazines that M4s or M16 rifles in the squad could take, the Marines banned the polymer PMAG for issue on November 26, 2012 to prevent interchangeability issues. In response, Magpul began the process of arranging verification and official testing for their improved PMAG 30 GEN M3 magazine, which is compatible with both the M27 and M16-series rifles. After Marine Corps testing of the M855A1 Enhanced Performance Round with the M27 showed reliability problems from feeding issues from standard magazines, the PMAG 30 GEN M3 Window, which had better reliability with the EPR, was approved for use by Marines in December 2016 so that M27 gunners who receive M855A1 rounds do not face such issues. Due to its role, high capacity magazines of between 50 and 100 rounds are being explored.
The M27 is essentially an HK416 with accessories required by the Marine Corps. The standard optic is the Trijicon ACOG Squad Day Optic (SDO), officially designated the Sight Unit, SU-258/PVQ Squad Day Optic. It is a 3.5×35 machine gun optic that has a Ruggedized Miniature Reflex (RMR) sight screwed on top for close-quarters engagements under 100 meters. Created for the SAW, the day optic offers slightly less magnification, but longer eye relief than the ACOG Rifle Combat Optic (RCO) on M16s and M4s. The longer relief helps reduce injury risk from recoil. It is issued with the Vickers Combat Applications sling and rail sling mounts, AIM Manta Rail Covers, Harris bipod, KAC backup iron sights, a foregrip, and bayonet lug. The M27 initially had a Grip Pod, which is a foregrip with bipod legs inside, but it was later replaced by a separate foregrip and bipod.
In January 2017, a USMC unit deployed with suppressors mounted to their M27 rifles as part of a concept to suppress every weapon in an infantry battalion. Exercises showed that having all weapons suppressed improved squad communication and surprise during engagements; disadvantages included additional heat and weight, increased maintenance, and the greater cost of equipping so many troops with the attachment. In July 2020, the Marine Corps announced it would be ordering suppressors for use by all M27s used by close combat units.
In late 2017, the Marine Corps began fielding an optimized version of the M27 which was given a new number, the: M38 designated marksman rifle (M38 DMR). Although certain selected M27s had been employed as marksman rifles since 2016, the M38 version outfits M27s selected for accuracy with a Leupold TS-30A2 Mark 4 MR/T 2.5-8x36mm variable power scope, the same optic fitted on the Mk 12 Special Purpose Rifle. The naming of the M38 followed a similar convention to the M27, being named after the 3rd Battalion, 8th Marines unit that tested the rifle out. By April 2018, fielding to all three Marine Expeditionary Forces had been completed. One M38 marksman version, fitted with a scope and QDSS suppressor, is to be fielded per infantry squad to hit targets at 600 meters. Full operational capability is planned for September 2018.
|Mass||7.9 lb (3.6 kg) empty
9.8 lb (4.4 kg) loaded weight with sling
|Length||36.9 to 33 in (940 to 840 mm) w/adjustable stock|
|Barrel length||16.5 in (420 mm)|
|Width||3.1 in (79 mm)|
|Height||9.4 in (240 mm)|
|Action||Gas-operated short-stroke piston, rotating bolt|
|Rate of fire||Sustained: 36 rpm
Cyclic: 700 to 900 rpm
|Effective firing range||600 m (point target)
800 m (area target)
|Maximum firing range||3,938 yd (3,601 m)|
|Feed system||30-round STANAG magazine|
|Sights||3.5× Squad Day Optic, flip-up rear rotary diopter sight and front post|