M27 Infantry Automatic Rifle
A U.S. Marine armed with an M27 IAR affixed with ACOG Squad Day Optic.
Type	Squad automatic weapon Assault rifle Designated marksman rifle
Place of origin	Germany
Service history
In service	2010–present
Used by	United States Marine Corps
Wars	Operation Enduring Freedom
Production history
Designer	Heckler & Koch
Designed	2008
Manufacturer	Heckler & Koch
Unit cost	US$3,000[1]
Produced	2010–present
No. built	4,153[2]
Specifications
Weight	7.9 lb (3.6 kg) empty 9.8 lb (4.4 kg) loaded weight with sling[3]
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)
Cartridge	5.56×45mm NATO
Action	Gas-operated short-stroke piston, rotating bolt
Rate of fire	Sustained: 36 rpm Cyclic: 700 to 900 rpm
Effective firing range	550 m (point target) 700 m (area target)[4]
Maximum firing range	3,938 yd (3,601 m)[4]
Feed system	30-round STANAG magazine
Sights	3.5x Squad Day Optic, flip-up rear rotary diopter sight and front post

The M27 Infantry Automatic Rifle(IAR) is a lightweight, magazine-fed 5.56mm, select-fire weapon based on the Heckler & Koch HK416. It is used by the United States Marine Corpsand 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. The United States Army does not plan to purchase the IAR.^[5][6][7] In December 2017, the Marine Corps revealed a decision to equip every Marine in an infantry squad with the M27.^[8]

History[edit]

Background[edit]

In 1985, the U.S. Marine Corps adopted the M249 Squad Automatic Weapon, one year after the U.S. Army. Procurement was a service-level decision because the weapon was adopted by the Army with a contract method the Marines could use. While the belt-fed M249 was portable and had a high volume of fire, its relatively heavy weight meant gunners could have trouble keeping up with riflemen.^[9]

IAR[edit]

In 1999, a Universal Need Statement was issued for an Infantry Automatic Rifle (IAR). Around 2000, the 1st Marine Division’s 2nd Battalion, 7th Marines Regiment conducted initial, limited IAR trials which confirmed the desirability of a light automatic rifle. Experiences in Iraq and Afghanistan resulted in formal requests for recommendations. The Universal Need Statement spent six years going through the procurement process before an official program was begun and a list of required capabilities was created in early 2005.^[9]
The Infantry Automatic Rifle program began on 14 July 2005, when the Marine Corps sent Requests For Information to arms manufacturers. Characteristics desired in the weapon included: portability and maneuverability; similarity in appearance to other rifles in the squad, reducing the likelihood that the gunner will receive special attention from the enemy; facilitation of the gunner’s participation in counter-insurgency operations and capability of maintaining a high volume of fire. An initial requirement for a magazine with a minimum capacity of 100 rounds was dropped in favor of the 30-round STANAG magazine because, at the start of testing, available 100-round magazines were unreliable. Caliber was specified as 5.56×45mm with non-linked ammunition, so as to achieve commonality with existing service rifles.^[9][10]
In 2006, contracts were issued to several manufacturers for sample weapons. Fabrique Nationale d’Herstal submitted an IAR variant of the FN SCAR, Heckler & Koch submitted an HK416 variant, and Colt Defense submitted two designs. Companies that attempted to compete but were not accepted as finalists for testing included the Land Warfare Resources Corporation M6A4 IAR,^[11][12] Patriot Ordnance Factory,^[6] and General Dynamics Armament and Technical Products with the CIS Ultimax 100 MK5 (marketed as the GDATP IAR).^[13]
In December 2009, the Heckler & Koch weapon won the competition and entered into a five-month period of final testing.^[14][15] In the summer of 2010, it was designated as the M27 Infantry Automatic Rifle,^[16] coincidentally sharing a designation with the 2nd Battalion, 7th Marines, who had been testing fully automatic rifles since 2001.^[17]

An M27 IAR displayed at the NDIAJoint Armaments Conference in May 2010.

While Marine Corps Systems Command was optimistic about operational testing, former Commandant of the Marine Corps General James T. Conway remained skeptical because of the reduction in firepower at the fireteam-level that would result if the M27 was adopted.^[18] He felt that, while more accurate, it was unlikely that the M27 could provide fire-superiority over the M249, a belt-fed LMG. A magazine-fed rifle, requiring frequent reloading, would not be able to sustain the same rate of fire. In a firefight, squad members carrying extra magazines for the M27 might not always be in position to supply them to the gunner. Further, the SAW was already a battle-proven weapon. It was also significant that the Army had chosen not to pursue the IAR concept.^[9]
After the Marine Corps Operational Test and Evaluation Activity conducted further testing at MCAGCC Twentynine Palms, Fort McCoy, and Camp Shelby (for dust, cold-weather, and hot-weather conditions, respectively), limited fielding of 458 IARs began to four infantry battalions (one per each Marine Expeditionary Force, one reserve) and one light armored reconnaissance battalion, all of which deployed to Afghanistan in 2011.^[19][20]
In May 2011, General James Amos of the U.S. Marine Corps approved the conclusion of the Limited User Evaluation (LUE), and ordered the replacement of the M249 LMG by the M27. Fielding of the approximately 6,500 M27 units was expected to be completed in the summer of 2013, at a cost of $13 million. Each M27 gunner was to be equipped with around twenty-two 30-round magazines of the type currently in use with the M16 and M4 carbineapproximating the combat load of an M249 SAW gunner; although the M27 gunner would not be expected to carry all 22 magazines. The individual combat load would be determined at the unit level and was expected to vary by unit, based on results of evaluations conducted by the four infantry battalions and one light armored reconnaissance battalion that participated in the Limited User Evaluation. Though program officials were aware that switching from the belt-fed M249 would result in a loss of suppressive fire capability, Charles Clark III, of the Marine Corps’ Combat Development and Integration Office, cited the substantially increased accuracy of the M27 as a significant factor in the decision to replace the M249.^[21]

Suppressive fire[edit]

A U.S. Marine practices firing an M27 IAR on fully automatic fire in April 2012.

The notion that the M27 represents a reduction in suppressive fire has spawned considerable debate between proponents of the M249 SAW within the infantry and those who advocate that a lighter, more maneuverable, and accurate weapon is sufficient to support offensive operations at the squad level. It is debatable, in fact, that program officials actually concede a loss of suppressive fire capabilities, as the only statements of concern over this concept were made by General Conway.
With a SAW, the doctrine of fire suppression is the sound of continuous fire with rounds landing close to the enemy. While the M249’s volume of fire may be greater, it is less accurate. Experienced troops who have dealt with incoming fire are less likely to take cover from incoming rounds if they are not close enough. With an IAR, the doctrine is that lower volume of fire is needed with better accuracy. Fewer rounds need to be used and automatic riflemen can remain in combat longer and in more situations.^[9]
Another benefit of the M27 over the M249 is that in many respects it resembles an M4 rifle as used by the rest of the squad. This makes it harder to identify by enemy troops.^[9]

Combat reviews[edit]

The IAR was initially fielded in December 2010.^[2] 1st Battalion 3rd Marines were deployed to Afghanistan in April 2011 with 84 IARs. Former SAW gunners initially did not like the M27, but appreciated it as time went on. It weighed 9 lb (4 kg) loaded, compared to 22 lb (10 kg) for an M249, which was a significant difference when on 5-hour long missions. Gunners said it was “two weapons in one,” being able to fire single shots accurately out to 800 meters and have fully automatic fire. It also blended in with standard M16-style service rifles, making it difficult for enemy forces to identify the machine gunner. The battalion leadership also saw the M27 as better at preventing collateral damage, as it is more controllable on fully automatic than the M249. Concern of volume of fire loss was made up for through training courses developed in December 2010. With the M249 SAW, the idea of suppression was volume of fire and the sound of the machine gun. With the M27 IAR, the idea of suppression shifts to engaging with precision fire, as it has rifle accuracy at long range and fully automatic fire at short range. Shooters transitioned from long-range precision fire at 700 meters to short-to-medium suppressive fire at 200 meters, both while in the prone position. Some gunners in combat have been used as designated marksmen. An M27 gunner with one aimed shot has the effect of three or four automatic shots from the SAW, and still has the option of a heavier volume with an accurate grouping.^[22]
Marines issued with the M27 enjoy its familiarity with the M4-style weapons in service. It is friendlier to troops due to its cleaner, lightweight system having fewer moving parts and jams. IAR gunners consider the rifle-grade accuracy to be a huge improvement over the SAW, despite the loss of sustained firing. With a shrinking budget, the Marine Corps is looking at ways to implement the IAR as a multipurpose weapon. Suggestions included use as an automatic rifle and as a designated marksman rifle,^[23] a role where it replaced the Squad Advanced Marksman Rifle.^[24] Additionally, the free-floating barrel offers improved accuracy at approximately 2 MOA compared with 4.5 MOA for M16A4 rifles.^[25]

Design[edit]

A U.S. Marine armed with an M27 fitted with a Harris bipod and a 3.5x Squad Day Optic covers his team in Afghanistan in March 2012.

The M27 is based on the Heckler & Koch HK416.^[26] 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.^[17] Alternate calibers other than 5.56 mm are being considered for the M27.^[9]

Use[edit]

The IAR is distributed one per four-man fireteam, three per squad, 28 per company, 84 per infantry battalion, and 72 per Light Armored Reconnaissance Battalion,^[27] with 4,476 total for the Marine Corps. The M249 was not completely replaced by the M27, and six of the machine guns are still issued to rifle companies.^[28]
In December 2017, the Marines revealed they would be equipping every Marine in an infantry squad with the M27, which would increase the number of rifles procured by at least 11,000. While not every Marine in a battalion will receive the weapon, others outside of squads are also being considered.^[8]

Magazine[edit]

The M27 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. While a rifleman normally carries seven 30-round magazines, an IAR gunner has to carry up to 16, and may carry as many as 21, 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.^[4] 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.^[29] 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.^[30] After Marine Corps testing of the M855A1 Enhanced Performance Round with the M27 showed reliability problems from feeding issues from standard magazines,^[31] 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.^[32] Due to its role, high capacity magazines of between 50 and 100 rounds are being explored.^[17]

Accessories[edit]

The M27 is essentially an HK416 with accessories required by the Marine Corps.^[33] 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.^[4][22] 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.^[34] 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.^[9]
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.^[35]

M38 DMR[edit]

In late 2017, the Marine Corps began fielding the M38 designated marksman rifle. Although certain M27s were employed as marksman rifles since 2016, the M38 version outfits the M27 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.^[36]