M27 IAR

The M27 Infantry Automatic Rifle is a select-fire 5.56mm weapon derived from the Heckler & Koch HK416, adopted by the United States Marine Corps to replace part of its M249 light machine gun fleet. The requirement dates to a Universal Need Statement of 1999 and trials conducted around 2000 by 2nd Battalion, 7th Marines, which confirmed the appeal of a light automatic rifle. The Infantry Automatic Rifle programme formally opened on 14 July 2005. The Marines wanted a weapon that was portable and manoeuvrable, that looked like the other rifles in the squad so that the automatic rifleman would not draw special attention from the enemy, and that could sustain a high volume of fire. An initial demand for a 100-round magazine was dropped in favour of the standard 30-round STANAG magazine, because the high-capacity magazines available at the time proved unreliable.

FN Herstal submitted a SCAR variant, Colt two designs and Heckler & Koch an HK416 derivative, which won the competition in December 2009 and was designated the M27 in summer 2010. After cold, hot and dust testing, 458 rifles were fielded to four battalions that deployed to Afghanistan in 2011. General James F. Amos approved the replacement of the M249 in May 2011, and roughly 6,500 M27s were delivered by 2013. The programme then expanded well beyond its original scope: in early 2017 Commandant General Robert Neller stated that he wanted every rifleman to carry one, and at SHOT Show 2018 the Corps confirmed an order for 11,000 more, making the M27 the standard service rifle of Marine infantry with the M4 retained only at platoon leadership level and above. Just over 14,000 were ultimately purchased.

The M27 is an HK416 fitted to Marine Corps requirements: a gas-operated short-stroke piston action with a rotating bolt and a 16.5-inch cold hammer-forged free-floating barrel, four MIL-STD-1913 rails on the handguard, and ambidextrous controls and charging handle that the standard HK416 did not receive until its A5 generation. The free-floating barrel gives roughly 2 MOA accuracy against about 4.5 MOA for the M16A4. The short-stroke piston runs cooler and cleaner than the direct-impingement M16 and M4, requiring less maintenance. The M38 Designated Marksman Rifle is a subvariant retaining most M27 features.

The switch provoked a lasting doctrinal argument. Former Commandant General James T. Conway and others held that a magazine-fed rifle could not match the suppressive volume of a belt-fed M249, that a gunner would need frequent reloads, and that the Army's refusal to pursue the concept was telling. Proponents countered that suppression through precision differs from suppression through volume: troops under fire take cover according to how close the rounds land, not how many there are. Field reports from 1st Battalion, 3rd Marines in Afghanistan in 2011 were favourable - the M27 weighs about 4 kg loaded against 10 kg for an M249, a decisive difference on long patrols, and gunners described it as "two weapons in one", accurate in single shots to 800 m and capable of automatic fire at close range while blending in visually with ordinary service rifles.