M27 Infantry Automatic Rifle

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[1]
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[2]
Produced 2010–present
Number built 4,153[3]
Weight 7.9 lb (3.6 kg) empty
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 850 rpm
Effective firing range 550 m (point target)
800 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 weapon used by the United States Marine Corps. It is intended to enhance an automatic rifleman's maneuverability, and it is based on the Heckler & Koch HK416. The U.S. Marine Corps is planning to purchase 6,500 M27s to replace a portion of the M249 light machine guns currently employed by automatic riflemen within Infantry and Light Armored Reconnaissance Battalions. Approximately 8,000–10,000 M249s will remain in service at the company level to be used at the discretion of company commanders. The United States Army does not plan to purchase the IAR.[5][6][7]



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, it was heavy for its role. Gunners could not keep pace with riflemen and the cumbersome light machine gun was not suited for Military Operations on Urban Terrain.[8]


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.[8]

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.[8][9]

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 a variant of the HK416). Colt Defense submitted two designs. Companies that attempted to compete, but were not accepted as finalists for testing, included Land Warfare Resources Corporation, which submitted the M6A4 IAR,[10][11] Patriot Ordnance Factory,[6] and General Dynamics Armament and Technical Products with the CIS Ultimax 100 MK5 (marketed as the GDATP IAR).[12]

In December 2009, the Heckler & Koch weapon won the competition and entered into a five-month period of final testing.[13][14] In the summer of 2010, it was designated as the M27 Infantry Automatic Rifle,[15] coincidentally sharing a designation with the 2nd Battalion, 7th Marines, who had been testing automatic rifles since 2001.[16]

An M27 IAR displayed at the NDIA Joint 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.[17] 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.[8]

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.[18][19]

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 carbine approximating the combat load of an M249 SAW gunner; although the M27 gunner would not 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.[20]

Suppressive fire

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.[8]

Beyond the increased accuracy another benefit of the M27 over the M249 is that it is in many respects a modified M4 rifle as used by the rest of the squad. This makes it far more suitable for operating indoors and in other cramped situations where its reduced size and weight make it faster and easier to handle. Although not ideal for close quarters fighting, it is far better in this function than the M249. The look of this is similar to the M4, so the gunner can hide in the group and has less chance of being deliberately targeted by the enemy.

Combat reviews

The IAR was initially fielded in December 2010.[3] 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 full 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 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 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.[21]

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,[22] a role where it replaced the Squad Advanced Marksman Rifle.[1] Additionally, the free-floating barrel offers improved accuracy at approximately 2 MOA compared with 4.5 MOA for M16A4 rifles.[23]


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.[24] It features a gas-operated short-stroke piston action with a rotating bolt. The free-floating barrel is surrounded by 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.[16] Alternate calibers other than 5.56 mm are being considered for the M27.[8]


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,[25] with 4,476 total for the Marine Corps.


The M27 draws ammunition from a standard 30-round STANAG magazine. Due to its role, high capacity magazines of between 50 and 100 rounds are being explored.[16] The M27 has been successfully test fired with the Armatac SAW-MAG 150-round drum magazine.[26] 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 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 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.[27] In response, Magpul began the process of arranging verification and official testing for their newer PMAG 30 GEN M3 magazine, which is compatible with both the M27 and M16-series rifles.[28]


The M27 is essentially an HK416 with accessories required by the Marine Corps.[29] 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][21] 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.[30] 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.[8]

See also



    1. 1 2 Marine brass endorses infantry plan to ditch M16 for M4 - Militarytimes.com, 27 July 2015
    2. The Marine Corps is Experimenting With a New Service Rifle - Military.com, 18 November 2016
    3. 1 2 West Coast Marines complete first M27 Designated Marksman Course - MarineCorpstimes.com, 18 February 2016
    4. 1 2 3 4 M27 First Impressions - Thefirearmblog.com, 20 April 2013
    5. Lamothe, Dan (February 4, 2009). "Marines to test, evaluate 4 auto-rifle models". Marine Corps Times. Retrieved 2 July 2010.
    6. 1 2 Cox, Matthew (September 15, 2008). "So long, SAW?". Marine Corps Times. Retrieved 2 July 2010.
    7. "Corps to Replace SAW With Automatic Rifle". Military.com. 2011. Retrieved 20 July 2011.
    8. 1 2 3 4 5 6 7 From BAR to IAR – How the Marines Finally Got Their Infantry Automatic Rifle - SAdefensejournal.com, 20 November 2012
    9. "10—Non-developmental, 5.56mm, Infantry Automatic Rifle (IAR)". FedBizOpp. July 14, 2005. Retrieved 20 August 2010.
    10. "M6A4". LWRC. 2009. Retrieved 2 July 2010.
    11. Richard Machowicz (15 November 2007). "Opening Round". Future Weapons. Season 3. Discovery Channel. Retrieved 3 February 2011.
    12. Crane, David (October 21, 2008). "GDATP IAR (Infantry Automatic Rifle)/Ultimax 100 MK5 LMG/SAW (Photos!)". Defense Review. Retrieved 2 July 2010.
    13. Lamothe, Dan (December 4, 2009). "H&K is frontrunner in IAR competition". Marine Corps Times. Retrieved 16 December 2009.
    14. Lamothe, Dan (December 3, 2009). "Corps chooses H&K to make SAW replacement". Marine Corps Times. Retrieved 20 August 2009.
    15. Lamothe, Dan (July 2, 2010). "Conway eyes additional testing for auto-rifle". Marine Corps Times. Retrieved 2 July 2010.
    16. 1 2 3 Marines swap firepower for accuracy with IAR - Marinecorpstimes.com, June 29, 2011
    17. Lamothe, Dan (April 19, 2010). "Corps may field infantry auto-rifle this fall". Marine Corps Times. Retrieved 19 April 2010.
    18. Lamothe, Dan (August 9, 2010). "SAW replacement set for real world testing". Marine Corps Times. Retrieved 10 August 2010.
    19. "Infantry Automatic Rifle: Update on a Marine Corps Priority Weapon System". MCOTEA Journal. United States Marine Corps. August 2009. p. 9. Retrieved 27 October 2010.
    20. "Corps to Replace SAW With Automatic Rifle". Military.com. 2011. Retrieved 16 July 2011.
    21. 1 2 IAR wins over skeptical Marine infantrymen - MarineCorpstimes.com, 19 July 2011
    22. M249 Light Machine Gun: Endangered species for Marines in Afghanistan - Dvidshub.net, November 12, 2012
    23. Sanborn, James K. (February 16, 2015). "Deadlier rifles and ammo may be on the way". Marine Corps Times. Gannett Company. Retrieved 21 February 2015. A free floating barrel could improve the M16A4 from a 4.5 minute-of-impact rifle to a 2 MOI rifle, putting it on par with the M27 Infantry Automatic Rifle, which uses a free floating barrel, said Chief Warrant Officer 5 Vince Pope, the Marine gunner who directs the Marksmanship Doctrine and Programs Management Section at Quantico.
    24. Crane, David (December 4, 2009). "U.S. Marine Corps Selects Heckler & Koch Infantry Automatic Rifle (HK IAR) Candidate as Replacement for FN M249 SAW/LMG". defensereview.com. Retrieved 20 August 2010.
    25. M27 IAR - Marinesmagazine.mil, May 16, 2012
    26. Armatac SAW-MAG for USMC’s HK M27 IAR - Defensereview.com, June 8, 2010
    27. Marine Corps bans popular rifle magazines - Marinecorpstimes.com, November 26, 2012
    28. Magpul speaks out on the Marine Corps polymer magazine ban - Militarytimes Gearscout.com, November 30, 2012
    29. Breakdown: M27 IAR vs. HK416 - Militarytimes.com/Gearscout, October 24, 2011
    30. The U.S. Marine Corps’ New M27 IAR - SAdefensejournal.com, September 10, 2012
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