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. This is the same key feature critical to the success of the HK416 rifles used by leading military and law enforcement customers.The MR556A1 is produced in the USA using American and German made components. The MR556A1 uses many of the same assemblies and accessories originally developed for the HK416 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. The HK rail system can be installed and removed with simple tools and returns to zero when reinstalled. The MR556A1 also has a Picatinny rail machined into the top of its upper receiver for mounting optics and mechanical sights. Unlike earlier prototypes, major sub assemblies,
