It is currently in use by some United States Special Operations Units as a replacement for the M4, and the Norwegian Armed Forces as a replacement for the AG3. It is also used by some European special operations forces, like the Polish GROM and the German KSK.
The HK416 is very similar to the M4 in appearance, but is different internally. The primary difference between this weapon and the M4 series is the short-stroke offset piston system, replacing the expanding gas inline piston system usually found in AR-pattern rifles. The mechanism of the rifle is actually closer to the H&K G36, rather than AR-pattern rifles. The HK416 has a slightly larger diameter bolt (.53 overall diameter (OD), as opposed to .512 OD) than the AR-15 does; an AR-15 bolt will fit in the HK416 carrier, rather loosely.
The HK416 has a quad rail to mount a variety of accessories and can mount the AG36 grenade launcher in seconds without any modifications. It also comes in a 7.62x51mm version called the HK417 which makes it a rival to the FN SCAR-L and FN SCAR-H that are currently in trials with US SOCOM. An HK416 upper receiver can fit on any AR-15 lower receiver without modification.
As the HK416's magazine well opening is flatter than other AR-15 derivatives, it reduces its compatibility with some STANAG magazine designs. The magazine well was later changed to have an angled opening in later iterations such as the HK416A5.
The HKM4 was the prototype version of the HK416, fitted with a fixed M16 stock and M4 fore-end, with a short CQB barrel. It was briefly marketed in the mid-2000s but did not see any sales. The design was revamped into the HK416 shortly afterward.
The HK416A5 is an improved variant of the HK416 that entered the Individual Carbine competition. The competition was cancelled without any winners. The HK416A5 has an angled magazine well, maximizing compatibility with other STANAG magazines such as Magpul PMAGs. The French army is replacing the FAMAS rifle with the HK416A5, designated as the HK416F.
The HK416A7 is similar to the A5 variant, designed for the German KSK and KSM. Its defining feature that sets it apart from other HK416 variants is its selector switch, which now only rotates 90 degrees instead of the 180 degrees on a typical AR pattern rifle.
The MR556 (MR223 in Europe) is a civilian variant of the HK416. Its main difference is that it features a semi-auto FCG instead of a select-fire FCG. There are other minor differences as well, but most of which can be reverted to the original look of the HK416, since the furniture is interchangeable.
M27 Infantry Automatic Rifle (IAR)
- Main article: M27 Infantry Automatic Rifle
Modified HK416 rifle developed for the United States Marine Corps Infantry Automatic Rifle program. This design won out, becoming the M27 IAR. So far, it is expected to act in the same capacity as the older M4A1, but also a variant with a heavier, longer barrel is expected to be a replacement for belt fed machine guns once field testing of the concept is completed.