H&K 51000385 MR556 Upper Receiver Kit 5.56mm for AR15/M16/M4

Transform your shooting experience with the H&K 51000385 MR556 Upper Receiver Kit. This kit symbolizes a revolutionary upgrade for your AR15, M16, or M4 platform, empowering you to harness the legendary reliability of Heckler & Koch's piston-driven system. The moment you integrate this powerhouse into your rifle, you will embark on a journey toward unparalleled performance, minimizing malfunctions and maximizing operational efficiency even in the most challenging environments.

Imagine a day at the range or out in the field where the only focus is on precision and accuracy, rather than constant cleaning and maintenance. The MR556 upper receiver kit replaces the traditional gas tube with a groundbreaking piston and pusher rod mechanism. This closed system effectively eliminates the buildup of hot carbon and destructive gases within your receiver area, keeping the essential components clean and functioning flawlessly. Your rifle will shoot smoother, cycle faster, and bring you a confidence that is indispensable when every shot counts.

Designed for the discerning shooter, the MR556 upper receiver kit captures the essence of what makes HK firearms undeniably trusted by elite military and law enforcement units around the world. Whether you are an avid competitor, tactical enthusiast, or a responsible defender, this upper receiver kit is your key to elevating your firearm’s capabilities. Feel the difference of reduced recoil and cleaner cycling the moment you fire. In tough situations, where reliability is paramount, the benefit of this upgrade shines brighter than ever.

Don’t settle for less when precision and power are just a modification away. With the included HK Soft case, you can transport your upgrade with ease and style, ensuring that your new upper receiver is always ready for action. Elevate your arsenal and experience the HK advantage firsthand with the MR556 Upper Receiver Kit. Your performance deserves nothing less than perfection.

Key Features

• Complete upper receiver/barrel assembly
• Upgrades AR-style rifles to HK piston system
• Piston and pusher rod mechanism reduces fouling
• Closed gas system eliminates direct-impingement issues
• Designed for AR15, M16, and M4 compatibility
• Comes with premium HK Soft case for transport

Technical Specifications

What's in the Box

• MR556 Upper Receiver Assembly
• 16.5-inch Barrel
• HK Soft Case

Compatibility & Requirements

• Must be compatible with Mil-Spec AR-platform lower receivers

Dimensions & Weight