HK UPPER MR556A4 5.56 16.5 BLK

The HK MR556A4 Upper Receiver in 5.56 caliber features a 16.5-inch barrel and a sleek black anodized finish, designed to enhance the performance of AR-15 style rifles. This upper assembly incorporates Heckler & Koch’s renowned piston and pusher rod system, replacing the conventional direct-impingement gas tube. By redirecting gases away from the receiver, this system reduces fouling and increases reliability under various shooting conditions.

Constructed with precision using both US and German components, the MR556A4 offers durability and consistent accuracy with a wide range of 5.56mm or .223 ammunition. Its updated barrel profile, adjustable gas block, and modern handguard reflect the latest refinements in HK’s design philosophy. The upper receiver is compatible with Mil-Spec AR-15 lowers and requires proper installation of Mil-Spec hammers on non-HK lowers to ensure reliable cycling.

Ideal for shooters seeking to upgrade their rifle with a high-quality upper receiver, the HK MR556A4 combines advanced engineering and proven components for dependable performance in a compact 16.5-inch platform.