Heckler & Koch MR556 A4 Upper Receiver Kit 16.5"

Heckler & Koch MR556 A4 Upper Receiver Kit

The MR556 A4 represents a significant upgrade to the AR-15 platform by introducing the proven piston-driven operating system that made the HK416 legendary among military and law enforcement professionals worldwide.

Key Features

• Piston-Driven System: Replaces the standard direct-impingement gas tube with a closed piston and pusher rod system
• Reduced Fouling: Eliminates hot carbon buildup and waste gases from entering the receiver, dramatically improving reliability
• 16.5" Barrel: Threaded 1/2x28 for suppressor or muzzle device compatibility
• M-LOK Handguard: Modern mounting system for tactical accessories
• A4 Improvements: Updated barrel profile, adjustable gas block, and refined ergonomics
• Complete Assembly: Includes bolt carrier group, charging handle, buffer weight, and buffer spring
• USA Assembled: Built in America using US and German-made components
• Anodized Finish: Durable black coating for corrosion resistance

Compatibility and Performance

This upper receiver kit allows you to retrofit any standard AR-15 lower receiver with HK's superior piston technology. The system functions reliably with a wide variety of quality 5.56 NATO or .223 Remington ammunition.

Important Note: Due to the shortened HK buffer and action spring, installation of Mil-Spec hammers on non-HK lower receivers is required for reliable function. These components are not compatible with fixed-stock AR/M16-type rifles.

What's Included

Your MR556 A4 upper receiver kit ships in an HK soft case for protection and transport.

Experience the same reliability that protects elite operators worldwide.