The HK416 is the standard assault rifle of the Norwegian Armed Forces and the United States Marine Corps (designated M27), and it has been selected by the French Armed Forces to replace the FAMAS and by the German Army to replace the G36 as the standard issue service rifle.

Other users include the Irish Army Ranger Wing, as well as the US Navy's SEAL Team Six, who used it to kill Osama bin Laden in 2011.

[3][4] The United States Army's Delta Force, at the request of R&D NCO Larry Vickers, collaborated with Heckler & Koch to develop a new carbine in the 1990s for use in close quarters combat.

The project was originally called the Heckler & Koch M4, but this was changed in response to a trademark infringement suit filed by Colt Defense.

[7] Delta Force replaced its M4s with the HK416D in March 2005, after tests revealed that the piston operating system significantly reduces malfunctions while increasing the life of parts.

A modified variant underwent testing by the United States Marine Corps as the M27 Infantry Automatic Rifle (IAR).

[12][13] The HK system uses a short-stroke piston driving an operating rod to force the bolt carrier to the rear.

[14] The reduction in heat and fouling of the bolt carrier group increases the reliability of the weapon and extends the interval between stoppages.

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.

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 as quickly as possible after being submerged in liquids like water.

[15] In July 2007, the U.S. Army announced a limited competition between the M4 carbine, FN SCAR, HK416, and the previously shelved HK XM8.

[22] 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.

[26][27] The French Armed Forces conducted a rifle evaluation and trial to replace the FAMAS, and selected the HK416F as its primary firearm in 2016.

[28][29] 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.

[33] The HK416 chambered for 5.56×45mm NATO is offered in multiple barrel lengths available to the military and law enforcement market only.

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, optimised magazine and ammunition compatibility, a repair kit housed inside the pistol grip, and a Flat Dark Earth colour scheme.

[39] It has a "heavy duty castle nut", which is more robust than the previous version, therefore making that weak spot more resistant to impact.

[43] The G95A1 is similar to the G95, but it features a height-adjustable shoulder support on the stock, a steeper grip angle as well as a shorter hand guard to comply with the required maximum weight of 3.5 kg (7.72 lb) according to the tender.

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.