MR556 A4 Upper Receiver Kit – 11″

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 in place of the gas tube normally found in AR15/M16/M4-style rifles — the same key feature critical to the success of the HK416.

The MR556 A4 Upper Receiver Kit is not classified as a firearm and can be purchased without an FFL. View full specs and dealer options on the official HK USA site.