Heckler & Koch MR556 A4 Complete AR-15 Upper Receiver - 5.56 - 16.5"

The Heckler & Koch MR556 A4 Complete AR-15 Upper Receiver retrofits a standard AR-style rifle with HK's short-stroke gas piston system, the same pusher-rod operating principle used in the HK416, for reduced carbon buildup and long-term reliability.

Features:

• 16.5" cold hammer forged barrel chambered in 5.56 NATO
• HK short-stroke gas piston operating system
• Adjustable gas block for suppressed or unsuppressed use
• HK Free Floating Rail System handguard
• Complete MR556 bolt carrier group included
• Extended convertible charging handle
• HK proprietary tungsten-filled buffer and buffer spring
• Soft transport case included

The short-stroke piston system keeps combustion gases out of the action entirely, cutting down on the carbon fouling that a direct-impingement system deposits inside the receiver over a hard day of shooting. The HK Free Floating Rail System handguard adds a stable mounting platform while reducing barrel deflection, and the adjustable gas block lets you tune cycling for suppressed or unsuppressed use.

This complete kit installs on any standard AR-style rifle receiver, giving you a plug-and-play upgrade path to piston operation without a full custom build or additional gunsmithing.

Heckler & Koch has supplied duty and military weapon systems worldwide for decades, and the MR556 brings HK416-derived piston technology to the civilian AR-15 market.