A direct descendant of the HK416, the MR556A1 is a semi-automatic rifle developed by HK as a premium level commercial/civilian firearm. 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 is produced in the USA from both American and German-made components. Additionally, subassemblies like the MR556A1’s upper receiver is fully interchangeable with other high quality AR-style firearms. This mdoel uses a barrel produced by HK’s famous cold hammer forging process using the highest quality steel to produce a long life barrel that provides superior performance with minimal degradation of accuracy and muzzle velocity after prolonged use.