M27 Infantry Automatic Rifle

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. 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]

M27 Infantry Automatic Rifle
A U.S. Marine armed with an M27 IAR affixed with ACOG Squad Day Optic.
TypeSquad automatic weapon
Automatic rifle
Assault rifle
Designated marksman rifle
Place of originGermany/United States
Service history
In service2010–present
Used byUnited States Marine Corps
WarsOperation Enduring Freedom
Production history
DesignerHeckler & Koch
ManufacturerHeckler & Koch
Unit costUS$1,300 [1]
No. built4,153[2]
Mass7.9 lb (3.6 kg) empty
9.8 lb (4.4 kg) loaded weight with sling[3]
Length36.9 to 33 in (940 to 840 mm) w/ adjustable stock
Barrel length16.5 in (420 mm)
Width3.1 in (79 mm)
Height9.4 in (240 mm)

Cartridge5.56×45mm NATO
ActionGas-operated short-stroke piston, rotating bolt
Rate of fireSustained: 36 rpm
Cyclic: 700 to 900 rpm
Effective firing range600 m (point target)
800 m (area target)[4]
Maximum firing range3,938 yd (3,601 m)[4]
Feed system30-round STANAG magazine
Sights3.5x Squad Day Optic, flip-up rear rotary diopter sight and front post


In 1985, the U.S. Marine Corps adopted the M249 Squad Automatic Weapon (SAW), one year after the U.S. Army. Procurement of this 22 lb (10.0 kg) loaded weight Light machine gun 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]

The M249 light machine gun provides infantry squads with the high rate of fire of a machine gun combined with accuracy and portability approaching that of a rifle. It can be fed from both linked ammunition and STANAG magazines, like those used in the M16 and M4. M249s have seen action in every major conflict involving the United States since the U.S. invasion of Panama in 1989.

Infantry Automatic Rifle (IAR)


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. The key difference between a lighter infantry rifle and a more heavily built automatic rifle is the ability of the latter to maintain sustained continuous fire without stoppages, overheating the barrel or receiver and losing accuracy. 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 (H&K) 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 H&K weapon won the competition and entered into a five-month period of final testing.[14][15] In the summer of 2010, it was formally 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]


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, Marine General James Amos 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 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.[20]

Replacement of M16/M4

In early 2017, Commandant of the Marine Corps General Robert Neller said he wanted to equip every "0311" rifleman with an M27 IAR. Because of that, the Marine Corps issued a request in early 2017 for 11,000 M27 IARs from H&K. While talking about the Corps' request, Chris Woodburn, deputy of the Maneuver Branch, Fires and Maneuver Integration at Marine Corps Combat Development Command, said "The new order will replace all M4s in every infantry squad with an M27, except for the squad leader." He also stated that the change includes infantry training battalions. The timeline for funding was planned for fiscal years 2019 and 2020, with the Corps acquiring some of the rifles in fiscal year 2018. As of August 2017, officials have stated that "riflemen are the top priority," but that the M27 "will be in the hands of combat engineers and light armored reconnaissance battalion scouts next." The Corps later issued a pre-solicitation notice for the M27. "The new pre-solicitation notice of 50,184 [M27s]," said Woodburn, "is [meant] to up the production capacity that H&K must be able to meet as the sole-source provider [of the M27], should the Marines decide to order more in the future." At SHOT Show 2018, the Marine Corps announced that the deal with H&K to produce 11,000 M27s for the Marine Corps had been finalized and that the M27 IAR would be adopted as the standard issue service rifle of the Marine Corps infantry, replacing the M4A1.[21]

Suppressive fire debate

While Marine Corps Systems Command was optimistic about operational testing, former Marine Commandant General James T. Conway remained skeptical because of the reduction in firepower at the fireteam-level that would result if the M27 was adopted.[22] He felt that, while more accurate, it was unlikely that the M27 could provide fire-superiority over the belt-fed M249 SAW. 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]

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

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 five hour 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.[23]

Marines issued with the M27 enjoy its familiarity with the M4-style weapons in service. Its gas-operated short-stroke piston action with a rotating bolt runs cooler, cleaner, requires less maintenance, has less internal parts wear and is less susceptible to malfunctions compared to previous direct impingement M4/M16 style weapons. 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,[24] a role where it replaced the Squad Advanced Marksman Rifle.[25] Additionally, the free-floating barrel offers improved accuracy at approximately 2 MOA compared with 4.5 MOA for M16A4 rifles.[26]


The M27 is based on the H&K HK416.[27] 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]


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.[28]

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,[29] 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.[30]


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.[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.[31] 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.[32] After Marine Corps testing of the M855A1 Enhanced Performance Round with the M27 showed reliability problems from feeding issues from standard magazines,[33] 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.[34] Due to its role, high capacity magazines of between 50 and 100 rounds are being explored.[17]


The M27 is essentially an HK416 with accessories required by the Marine Corps.[35] 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][23] 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.[36] 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.[37]


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.[38] 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.[39]

See also


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  4. M27 First Impressions Archived 2013-05-08 at the Wayback Machine - Thefirearmblog.com, 20 April 2013
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  6. Cox, Matthew (September 15, 2008). "So long, SAW?". Marine Corps Times. Archived from the original on 6 July 2010. Retrieved 2 July 2010.
  7. "Corps to Replace SAW With Automatic Rifle". Military.com. 2011. Archived from the original on 18 July 2011. Retrieved 20 July 2011.
  8. M27s and 'Head-to-Toe' Gear Overhaul on the Way for Marine Grunts Archived 2018-01-07 at the Wayback Machine - Military.com/Kitup, 5 January 2018
  9. From BAR to IAR – How the Marines Finally Got Their Infantry Automatic Rifle Archived 2013-10-31 at the Wayback Machine - SAdefensejournal.com, 20 November 2012
  10. "10—Non-developmental, 5.56mm, Infantry Automatic Rifle (IAR)". FedBizOpp. July 14, 2005. Archived from the original on 22 November 2011. Retrieved 20 August 2010.
  11. "M6A4". LWRC. 2009. Archived from the original on 5 September 2012. Retrieved 2 July 2010.
  12. Richard Machowicz (15 November 2007). "Opening Round". Future Weapons. Season 3. Discovery Channel. Archived from the original on 2 February 2012. Retrieved 3 February 2011.
  13. Crane, David (October 21, 2008). "GDATP IAR (Infantry Automatic Rifle)/Ultimax 100 MK5 LMG/SAW (Photos!)". Defense Review. Archived from the original on 15 June 2010. Retrieved 2 July 2010.
  14. Lamothe, Dan (December 4, 2009). "H&K is frontrunner in IAR competition". Marine Corps Times. Archived from the original on 2012-03-22. Retrieved 16 December 2009.
  15. Lamothe, Dan (December 3, 2009). "Corps chooses H&K to make SAW replacement". Marine Corps Times. Archived from the original on 7 December 2009. Retrieved 20 August 2009.
  16. Lamothe, Dan (July 2, 2010). "Conway eyes additional testing for auto-rifle". Marine Corps Times. Archived from the original on 14 July 2011. Retrieved 2 July 2010.
  17. Marines swap firepower for accuracy with IAR Archived 2013-10-19 at the Wayback Machine - Marinecorpstimes.com, June 29, 2011
  18. Lamothe, Dan (August 9, 2010). "SAW replacement set for real world testing". Marine Corps Times. Archived from the original on 8 March 2012. 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. Archived from the original on 18 July 2011. Retrieved 16 July 2011.
  21. Marines want 11,000 Infantry Automatic Rifles to replace M4 in every infantry squad Archived 2018-03-31 at the Wayback Machine - Marinesmagazine.mil, 15 August, 2017
  22. Lamothe, Dan (April 19, 2010). "Corps may field infantry auto-rifle this fall". Marine Corps Times. Archived from the original on 8 March 2012. Retrieved 19 April 2010.
  23. IAR wins over skeptical Marine infantrymen Archived 2013-10-21 at the Wayback Machine - MarineCorpstimes.com, 19 July 2011
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  26. Sanborn, James K. (February 16, 2015). "Deadlier rifles and ammo may be on the way". Marine Corps Times. Gannett Company. Archived from the original on 8 July 2017. 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.
  27. 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. Archived from the original on 29 July 2012. Retrieved 20 August 2010.
  28. No More M4 — USMC Adopts H&K M27 Infantry Automatic Rifle Archived 2018-03-31 at the Wayback Machine - bulletin.accurateshooter.com, February 2, 2018
  29. M27 IAR Archived 2013-02-04 at the Wayback Machine - Marinesmagazine.mil, May 16, 2012
  30. The Corps' quest for the best rifle for infantrymen Archived 2017-06-18 at the Wayback Machine - MarineCorpstimes.com, April 2, 2017
  31. Marine Corps bans popular rifle magazines Archived 2012-11-30 at the Wayback Machine - Marinecorpstimes.com, November 26, 2012
  32. Magpul speaks out on the Marine Corps polymer magazine ban Archived 2012-12-04 at the Wayback Machine - Militarytimes Gearscout.com, November 30, 2012
  33. Army Round Triggers Problems in Marine M27 Auto Rifle Archived 2016-12-26 at the Wayback Machine - Military.com, 20 December 2016
  34. Marines to Get PMAG to Fix M27 Woes with M855A1 Round Archived 2016-12-26 at the Wayback Machine - Kitup.Military.com, 20 December 2016
  35. Breakdown: M27 IAR vs. HK416 Archived 2012-09-06 at the Wayback Machine - Militarytimes.com/Gearscout, October 24, 2011
  36. The U.S. Marine Corps’ New M27 IAR Archived 2013-10-12 at the Wayback Machine - SAdefensejournal.com, September 10, 2012
  37. Marine Unit in Norway First to Deploy with Rifle Suppressors Archived 2017-05-15 at the Wayback Machine - Military.com, 11 May 2017
  38. USMC Fields Heckler & Koch M27 as M38 Designated Marksman Rifle Archived 2017-12-31 at the Wayback Machine - Thefirearmblog.com, 29 December 2017
  39. The Corps is on track to fully field the M38 marksman rifle, despite setbacks for the M27 IAR Archived 2018-04-28 at the Wayback Machine. Marine Corps Times. 27 April 2018.
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