Heckler and Koch MR556 A4 Upper Receiver/Barrel Assembly 5.56 11″ Barrel

Heckler & Koch MR556 A4 11″ Upper Receiver Features

Optimized for suppressed and CQB applications, the 11-inch MR556 A4 upper is built around HK’s short-stroke gas piston system with an adjustable gas block, enabling smooth function with or without a suppressor. The 1/2×28 threaded barrel is concentric and precision-machined, ensuring compatibility with muzzle devices and suppressors.

It includes a monolithic M-LOK handguard with integrated ambidextrous QD sling cups, a continuous Picatinny rail for optics and sights, and an ambidextrous charging handle with dual claw extensions. The match-grade cold hammer-forged barrel provides outstanding accuracy and barrel life, while the included bolt carrier group, charging handle, buffer weight, and buffer spring make this upper fully operational out of the box.

Heckler & Koch MR556 A4 11″ Upper Receiver Specifications

• Manufacturer: Heckler & Koch (HK)
• Model: MR556 A4 Upper Receiver
• Series: MR556
• Category: Uppers
• Caliber: .223 Remington / 5.56 NATO
• Barrel Length: 11″
• Thread Pattern: 1/2×28
• Firearm Fit: AR-15 Lower Receivers
• Handguard: M-LOK Interface with Integral Ambi QD Cups
• Rail: Continuous Picatinny (Upper to Handguard)
• Charging Handle: Extended Ambidextrous with Dual Claws
• Barrel Type: Match-Grade Cold Hammer-Forged
• Gas System: Adjustable Regulator (Suppressed/Unsuppressed)
• Finish: Anodized
• Color: Black
• Includes: Bolt Carrier Group, Charging Handle, Buffer Weight, Buffer Spring