The HK MR556 Competition Model is a civilian semi-automatic rifle developed to be an improvement over conventional AR-type carbines and rifles. Its 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. Unlike its predecessor the HK416, the MR556A1 does not use a chrome-lined barrel. Chrome-lining can sometimes mask bore imperfections and negatively affect accuracy. For the new series of Heckler & Koch semi-automatic MR rifles, HK designers and engineers believe best accuracy comes with an unlined bore
Designed to function with a wide variety of high quality 5.56 ammunition, the MR556A1 uses a CIP approved chamber. The MR556A1 also functions reliably with most quality Caliber .223 ammunition. The MR556A1 is being produced with the same commitment to quality as all HK firearms. By using joint U.S./German manufacturing, Heckler & Koch leverages the relative strengths of two continents to make the preeminent AR-type firearm, combining the designs innovations of the USA and Germany into one new product.