M27 Infantry Automatic Rifle

The M27 is the answer the United States Marine Corps gave to a question nobody else was asking: what if the automatic rifleman in a fire team carried something that looked and handled exactly like everybody else’s rifle. Heckler & Koch won the Infantry Automatic Rifle competition in December 2009 with a version of the HK416, and the weapon was designated in the summer of 2010.

The requirement is what makes the rifle interesting, because most of it is about not standing out. The Marine Corps asked in 2005 for portability, for similarity in appearance to the other rifles in the squad, and for the ability to keep up a high volume of fire; an early demand for a magazine of at least a hundred rounds was dropped in favour of the standard thirty-round STANAG box. What the M27 gives up against the belt-fed M249 it was bought to replace is exactly what a magazine gives up against a belt, and the trade is deliberate: a 3.58 kg rifle firing from a closed bolt, with a 16.5-inch barrel, instead of a belt-fed open-bolt machine gun twice its weight. The sustained rate is quoted at 36 rounds a minute, a sixth of what the cyclic rate suggests, and that number is the honest measure of the compromise.

Underneath it is HK’s short-stroke gas piston rather than the AR-15’s direct impingement, so the carrier is driven by a rod and an operating pusher instead of by gas admitted into the receiver. That is the HK416’s contribution; almost everything the Marine sees and touches is the AR-15’s.

The programme then went somewhere it was never intended to. Fielding began with 458 rifles to five battalions bound for Afghanistan in 2011; by 2019 the Corps had bought 14,100 and had decided to issue the M27 to every infantry rifleman in place of the M16A4 and the M4A1, turning an automatic rifle into a service rifle. A variant with a variable-power optic and a suppressor is issued one per squad as the M38 designated marksman rifle.

Gaps on this page: no sight radius, trigger pull or rifling twist is published for the M27 in any free source, and the barrel is recorded only by length. The 14,100 figure is what the Marine Corps had bought by April 2019, not a production total; the $1,300 unit cost is a 2018 contract price to the government, not a retail one. The cyclic rate is published as a 700-to-900-rounds-a-minute range and is recorded here as its midpoint, marked estimated. The 11-inch barrel issued with the Reconnaissance Weapons Kit is noted but not modelled as a variant, because no separate weight or overall length is published for it.