A direct descendent of the HK416, the MR556A1 is a semi-automatic rifle developed by Heckler & Koch as a premium level commercial/civilian firearm. Like the HK416, the MR556A1 is a major product improvement of conventional AR-type carbines and rifles. Using the HK- proprietary gas piston system found on the HK416 and G36, the MR556A1 does not introduce propellant gases and carbon fouling back into the rifle's interior, making it the most reliable of any AR-type firearm. The MR556A1 uses many of the same assemblies and accessories originally developed for the HK416 including the HK free-floating four-quadrant rail system. This handguard system allows all current accessories, sights, lights, and aimers used on M4/M16-type weapons to be fitted to the MR rifles. The HK rail system can be installed and removed without tools and returns to zero when reinstalled. The MR566A1 will be produced in the USA from both American and German-made components. Additionally, subassemblies like the MR556A1's upper receiver will be fully interchangeable with other high quality AR-style firearms. Like the famous HK416, the MR556A1 uses a barrel produced by Heckler & Koch's famous cold hammer forging process. The highest quality steel is used in this manufacturing process, producing a long life barrel that provides superior performance with minimal degradation of accuracy and muzzle velocity after prolonged use.