Product Features & Specifications

HK 51000385 MR556 Upper Receiver Kit 5.56mm for AR15/M16/M4

This kit includes a complete upper receiver/barrel assembly, allowing Mil-Spec 5.56mm AR-style rifles to be retrofitted to HK's piston and pusher rod system. This system utilises a piston and a pusher rod in place of the gas tube normally found in AR15/M16/M4-style rifles.

This closed system virtually eliminates the malfunctions common in direct-impingement gas systems, as hot carbon fouling and waste gases are not propelled into the receiver area to operate the action. This is the same key feature critical to the success of the HK416 used by elite military and law enforcement customers.

Upper will ship in a HK Soft case.