A direct descendant of the HK416, the MR556A1 is a semi-automatic rifle developed by Heckler & Koch as a premium level commercial/civilian firearm with match rifle capability. Like the HK416, the MR556A1 is a major product improvement over conventional AR-type carbines and rifles. The MR556A1 uses the HK proprietary gas piston operating system, employing a piston and a solid operating "pusher" rod in place of the gas tube normally found in AR15/M16/M4-style firearms. This method of operation virtually eliminates malfunctions that are common to direct impingement gas systems since hot carbon fouling and waste gases do not enter the receiver area. It uses many of the same assemblies and accessories including the HK free-floating four-quadrant rail system. The HK Free Floating Rail System (FFRS) handguard has four MIL-STD-1913 "Picatinny" rails and allows all current accessories, sights, lights, and aimers used on M4/M16-type arms to be fitted to the MR Series. It features a German-made barrel produced by Heckler & Koc's famous cold hammer forging process. The highest quality steel is used in this unique manufacturing process producing a barrel that provides superior accuracy and long service life. A precise enhanced two-stage trigger adds significantly to the accuracy of the MR556A1 and an extended latch charging handle makes operating the rifle with a telescopic sight easier. The retractable buttstock can be locked into a solid, non-moving position by tightening an Allen screw
