Using AR-15 platform Heckler & Koch manufactured HK416 as an improvement to the Colt M4 carabine with inclusion of gas–piston system derived from H&K G36. This design prevents combustion gases from entering the weapon’s interior, a shortcoming with direct impingement systems. The reduction in heat and fouling of the bolt carrier group increases the reliability of the weapon and extends the interval between stoppages. The barrel is cold hammer forged for better firing sesions.
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. HK 416 is equipped with Picatinny rail forearm on four sides alowing it to be mounted with most current accessories. Pistol grip is designed by H&K with a selection of interchangeable trigger groups allow for safe semi-automatic and fully automatic options. HK416 includes a folding front sight, and a rear sight similar in design to the G3.
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, andCamp 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, CA, First Battalion, 3rd Marines, out of Marine Corps Base HI, 1st Battalion, 9th Marines, out of Camp Lejeune, NC; and 1st Battalion, 25th Marines, out of Fort Devens, MA have deployed the weapon.
The HK416 models chambered for 5.56×45mm NATO available to the military and law enforcement market are:
- D10RS: sub-compact with a 264 mm (10.4 in) barrel
- D14.5RS: carbine rifle 368 mm (14.5 in) barrel
- D16.5RS: rifle with 419 mm (16.5 in) barrel
- D20RS: full-sized rifle 505 mm (19.9 in) barrel