The HK416 was originally developed as an improvement to the traditional, direct impingement style carbines in use by military and police. Utilizing a short stroke gas piston and improved carrier, the 416 has proven popular with elite military units and law enforcement angencies world wide. The commerical version of the rifle, the MR556, shares many of these same improvements. With this upper receiver kit, you can experience the improved operating system of the HK416 at a fraction of the cost of a complete rifle.
The MR556A1 Upper Receiver Kit includes a complete upper receiver/barrel assembly, bolt carrier assembly, buffer, and buffer spring allowing most high-quality 5.56 mm AR-style rifles to be retrofitted to HKs pusher rod system. The Upper Receiver Kit is the core of the HK 5.56 mm proprietary gas piston operating system. It employs a piston and a solid operating pusher rod in place of the gas tube normally found in AR15/M16/M4-style firearms.
The same operating system is used in the combat-proven 5.56 mm HK416 as well as the G36, XM8, HK417, and a variety of other Heckler & Koch arms. The MR556A1 Upper Receiver Kit is designed to be fully interchangeable with all high quality AR-style firearms, simply by attaching it to an AR lower receiver using the standard takedown pins. Due to the shortened length of the HK buffer and HK (action) buffer spring, these parts do not work in fixed stock AR-type rifles. Installation of MIL-SPEC hammers in non-HK lower receivers is required for reliable function. Additionally, the MR556A1 Upper Receiver Kit does not work in lower receivers with fully automatic or selective fire mechanisms.
The HK piston driven operating system virtually eliminates malfunctions that are common to direct impingement ga s 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 Upper Receiver Kit is produced in the USA using American and German made components. The Upper Receiver Kit uses a German-made barrel produced by Heckler & Kochs famous cold hammer forging technology. The highest quality steel is used in this unique manufacturing process producing a barrel that provides superior accuracy and long service life.
Specifications and Features:
Complete MR556 upper receiver/barrel assembly
16.5″ cold-hammer forged barrel
Upper receiver with forward assist
Extended convertible charging handle
HK free floating rail system handguard
Complete MR556 bolt group assembly
Tungsten filled HK proprietary buffer
HK proprietary buffer (action) spring