Heckler & Koch MR556 A4 Upper Receiver Kit 5.56 NATO 16.5" Barrel

The Heckler & Koch MR556 A4 Upper Receiver Kit is a complete upper receiver and barrel assembly for AR-15 pattern rifles, built to convert a Mil-Spec 5.56mm AR-style rifle to HK's piston and pusher rod operating system. The piston and pusher rod replace the direct-impingement gas tube, which HK states keeps hot carbon fouling and propellant gases out of the receiver area.

The kit is chambered in 5.56x45mm NATO and .223 Remington and features a 16.5-inch cold-hammer forged barrel with a black anodized finish. Included components are a forward assist, an extended convertible charging handle, an HK Free Floating Rail System handguard, a complete MR556 bolt group, a tungsten-filled HK proprietary buffer and action spring, and an adjustable gas block. The upper ships in an HK soft case.

• Fits: AR-15 pattern lower receivers
• Caliber: 5.56x45mm NATO, .223 Remington
• Barrel Length: 16.5 inches
• Barrel: Cold-hammer forged
• Finish: Anodized black
• Operating System: Piston and pusher rod
• Handguard: HK Free Floating Rail System
• Package: Upper receiver kit in HK soft case