The Heckler & Koch HK416 is a rifle designed and manufactured by Heckler & Koch. Although its design is based on the AR-15 class of weapons, specifically the Colt M4 carbine family issued to the U.S. military, it uses a proprietary short-stroke gas piston system derived from the ArmaLite AR-18 (the same system was also used in Heckler & Koch's earlier G36 family of rifles). It is the standard assault rifle of the Norwegian Armed Forces, selected by the French Armed Forces to replace the FAMAS, and was the weapon used by SEAL Team Six to kill Osama Bin Laden in 2011.^[2][3]

The United States Army's Delta Force, at the request of R&D NCO Larry Vickers, collaborated with the German arms maker Heckler & Koch to develop the new carbine in the early 1990s. During development, Heckler & Koch capitalized on experience gained developing the Bundeswehr's Heckler & Koch G36 assault rifle, the U.S. Army's XM8 rifle project (cancelled in 2005) and the modernization of the British Armed Forces SA80 small arms family. The project was originally called the Heckler & Koch M4, but this was changed in response to a trademark infringement suit filed by Colt Defense.

Delta Force replaced its M4s with the HK416 in 2004, after tests revealed that the piston operating system significantly reduces malfunctions while increasing the life of parts.^[4] The HK416 has been tested by the United States military and is in use with some law enforcement agencies. It has been adopted as the standard rifle of the Norwegian Armed Forces (2008) and the French Armed Forces (2017) and is used by many special operations units worldwide.

A modified variant underwent testing by the United States Marine Corps as the M27 Infantry Automatic Rifle. After the Marine Corps Operational Test & Evaluation Activity supervised a round of testing at MCAGCC Twentynine Palms, Fort McCoy, and Camp Shelby (for dust, cold-weather, and hot-weather conditions, respectively). As of March 2012, fielding of 452 IARs has been completed of 4,748 ordered. Five infantry battalions: 1st Light Armored Reconnaissance Battalion and 2nd Battalion, 4th Marines, out of Camp Pendleton, Calif.; First Battalion, 3rd Marines, out of Marine Corps Base Hawaii; 1st Battalion, 9th Marines, out of Camp Lejeune, N.C.; and 1st Battalion, 25th Marines, out of Fort Devens, Mass. have deployed the weapon.^[5][6] In December 2017, the Marine Corps revealed a decision to equip every Marine in an infantry squad with the M27.^[7]

The HK416 uses a HK-proprietary short-stroke gas piston system that derives from the HK G36, forgoing the concentric to bore gas piston system standard in AR-15 rifles.^[8][9] The HK G36 gas system was in turn partially derived from the AR-18 assault rifle designed in 1963.^[10] The HK system uses a short-stroke piston driving an operating rod to force the bolt carrier to the rear. This design prevents combustion gases from entering the weapon's interior—a shortcoming with direct impingement systems.^[11] The reduction in heat and fouling of the bolt carrier group increases the reliability of the weapon and extends the interval between stoppages. During factory tests the HK416 fired 10,000 rounds in full-auto without malfunctioning.^[12]

The HK416 is equipped with a proprietary accessory rail forearm with MIL-STD-1913 rails on all four sides. This lets most current accessories for M4/M16-type weapons fit the HK416. The HK416 rail forearm can be installed and removed without tools by using the bolt locking lug as the screwdriver. The rail forearm is "free-floating" and does not contact the barrel, improving accuracy.

The HK416 has an adjustable multi-position telescopic butt stock, offering six different lengths of pull. The shoulder pad can be either convex or concave and the stock features a storage space for maintenance accessories, spare electrical batteries or other small kit items. It can also be switched out for other variations like Magpul stocks.

The trigger pull is 34 N (7.6 lbf). The empty weight of a HK416 box magazine is 250 g (8.8 oz).

The HK416's barrel is cold hammer-forged with a 20,000-round service life and features a 6 grooves 178 mm (7 in) right hand twist. The cold hammer-forging process provides a stronger barrel for greater safety in case of an obstructed bore or for extended firing sessions. Modifications for an over-the-beach (OTB) capability such as drainage holes in the bolt carrier and buffer system are available to let the HK416 fire safely after being submerged in water.

In July 2007, the U.S. Army announced a limited competition between the M4 carbine, FN SCAR, HK416, and the previously-shelved HK XM8. Ten examples of each of the four competitors were involved. Each weapon fired 60,000 rounds in an extreme dust environment. The shoot-off was for assessing future needs, not to select a replacement for the M4.^[13][14] The XM8 scored the best, with only 127 stoppages in 60,000 total rounds, the FN SCAR Light had 226 stoppages, while the HK416 had 233 stoppages. The M4 carbine scored "significantly worse" than the rest of the field with 882 stoppages.^[4] However, magazine failures caused 239 of the M4's 882 failures. Army officials said, in December 2007, that the new magazines could be combat-ready by spring of 2008 if testing went well.^[15]

In December 2009, a modified version of the HK416 was selected for the final testing in the Infantry Automatic Rifle program, designed to partially replace the M249 light machine gun at the squad level for the United States Marine Corps.^[16] It beat the three other finalists by FN Herstal and Colt Defense. In July 2010, the HK416 IAR was designated as the M27, and 450 were procured for additional testing.^[17]

The Turkish company Makina ve Kimya Endustrisi Kurumu ("Mechanical and Chemical Industry Corporation") has considered manufacturing a copy of the HK416 as the MKEK Mehmetçik-1 for the Turkish Armed Forces.^[18] Instead, the new MPT-76 rifle has been developed by KALEKALIP with MKEK as the producer, with the Mehmetçik-1 dropped from adoption into the Turkish military.^[19][20]

The French armed forces conducted a rifle evaluation and trial to replace the FAMAS, and selected the HK416F as its primary firearm in 2016.^[21][22] Of the 93,080 rifles, 54,575 will be a "short" version with a 280 mm (11 in) barrel weighing 3.7 kg (8.2 lb) without the ability to use a grenade launcher, and 38,505 will be a "standard" version with a 368 mm (14.5 in) barrel weighing 4 kg (8.8 lb), of which 14,915 will take FÉLIN attachments; standard rifles will be supplied with 10,767 HK269F grenade launchers. 5,000 units are supposed to be delivered in 2017, half of the order delivered by 2022, and the order fulfilled by 2028.^[23] The first batch of 400 rifles was delivered on 3 May 2017.^[24]

The HK416 was one of the weapons displayed to U.S. Army officials during an invitation-only Industry Day on November 13, 2008. The goal of the Industry Day was to review current carbine technology prior to writing formal requirements for a future replacement for the M4 carbine.^[25][26] The HK416 was then an entry in the Individual Carbine competition to replace the M4. The weapon submitted was known as the HK416A5.^[27] It features a stock similar to that of the G28 designated marksman rifle, except slimmer and non-adjustable. The rifle features an improved tool-less adjustable gas regulator for suppressor use, which can accommodate barrel lengths down to 267 mm (10.5 in) without modifications. It also features a redesigned lower receiver with ambidextrous fire controls, optimized magazine and ammunition compatibility, a repair kit housed inside the pistol grip, and a Flat Dark Earth color-scheme.^[28] The stock has a fixed buttplate and no longer has a storage space, as well as the sling loops removed from it. The V2 HK Battle grip is incorporated, which has the V2 grip profile with the storage compartment of the V1 grip for tools. The handguard uses a new hexagonal-shaped cross bolt that cannot be removed by the bolt locking lugs, but instead by the takedown tool housed inside the grip.^[29] It has a "heavy duty castle nut", which is more robust than the previous version, therefore making that weak spot more resistant to impact. The Individual Carbine competition was cancelled before a winning weapon was chosen.^[30]

Civilian variants of the HK416 and HK417 introduced in 2007 were known as MR223 and MR308 (as they remain known in Europe). Both are semi-automatic rifles with several "sporterized" features. At the 2009 SHOT Show, these two firearms were introduced to the U.S. civilian market renamed respectively MR556 and MR762.^[33] There is another variant of the MR556 called the MR556A1, which is an improved version of the former.^[34] It was created with input from American special forces units.^[35] The MR556A1 lets the upper receiver attach to any M16/M4/AR-15 family lower receiver, as the receiver take-down pins are in the same standard location. The original concept for the MR556 did not allow for this, as the take-down pins were located in a "non-standard" location. The MR223 maintains the "non-standard" location of the pins, disallowing attachment of the upper receiver to the lower receivers of any other M16/M4/AR-15 family of rifles. As of 2012, the MR556A1 upper receiver group fits standard AR-15 lower receivers without modification, and functions reliably with standard STANAG magazines. HK-USA sells a variant under the MR556A1 Competition Model nomenclature; it comes with a 14.5" free-float Modular Rail System (MRS), 16.5" barrel, OSS compensator and Magpul CTR buttstock. The firearm's precision is specified as 1 MOA by Heckler & Koch. In Europe, the MR223A3 variant is sold with the same cosmetic and ergonomical improvements of the HK416A5. The French importer of Heckler & Koch in France, RUAG Defence, have announced that they are going to sell two civilian versions of the HK416F, named the MR223 F-S (14.5″ Standard version) and MR223 F-C (11″ Short version).^[36]