By adapting a short-stroke gas piston operating system to the traditional direct gas impingement AR-15/M16 design, Heckler & Koch created the HK416 rifle, which has been adopted by elite military and law enforcement units around the world. Versions in 5.56 NATO and 7.62 NATO also serve the U.S. military as the M27, M38 and M110A1 Compact Semi-Automatic Sniper System (CSASS). Semi-automatic versions for the U.S. civilian market were introduced in 2009 as the MR556 and MR762. New for 2024, as part of the company’s relaunched HK-USA division, they are introducing new A4 versions of the MR556 and MR762.
The MR556 and MR762 are civilian versions of the HK416/417, as used by the U.S. military and other elite military and law enforcement organizations around the world.
The A4 series of firearms use the multi-lug, rotating bolt operated by a short-stroke gas-piston system of the original HK416/MR556, housed in aluminum alloy upper and lower receivers. Beyond this, improvements abound. A new tensioning buffer improves fit between upper and lower receivers. The gas block is adjustable for both suppressed and unsuppressed usage. Controls include ambidextrous bolt release and magazine release buttons, as well as the safety lever with 45-degree throw, all of which are present on both sides of the receiver, and the charging handle is also ambidextrous.
The magazine well has a new angle designed for reliable feeding with the wide variety of magazines on the market. A 30-round magazine is supplied with the MR556 and a 20-round magazine with the MR762. Versions with a 10-round magazine are also available for customers who are restricted by local laws.
The A4 version of the MR556 includes many improvements for the American market, including fully-ambidextrous controls and upgraded furniture.
Furniture has been updated with a new slimline aluminum handguard that allows the barrel to free-float providing both M-Lok slots and sockets for QD attachments, an ergonomic pistol grip and HK416-style slimline buttstock. The match-grade barrel is made from cold hammer-forged, cannon-grade steel and its bore has a lifetime warranty. Rifling is six-groove with a 1:7” twist for the MR556 and the MR762 uses four-groove rifling with a 1:11” twist. Muzzles are threaded 1/2x28 TPI for the MR556 and 5/8x24 TPI on the MR762.
For the first time, HK USA is offering the MR556 in pistol format.
The A4 treatment is applied to both the “small frame” (556) and “large frame” (762) MR designs. In the 5.56 NATO-chambered MR556, A4 versions are available in both pistol and rifle configurations. The rifle version has a 16.5” barrel for an overall length of 36.5” with the stock fully extended and weight of 7.67 lbs., while the pistol version uses an 11” barrel and has a receiver extension for attaching arm braces or other accessories, with an overall length of 26.5” and weight of 6.61 lbs. The 7.62 NATO MR762 A4 has an overall length of 39.5” with a 16.5” barrel and weighs 9.84 lbs.
The large-frame MR762, chambered in 7.62 NATO, is also given the A4 treatment.
The MR556 A4 rifle and pistol have an MSRP of $3,999, while the MR762 A4 rifle retails for $4,749. California compliant versions of both rifles are $50 more. For more information, see the company’s website.
