HK MR556 A4 | 5.56 NATO | 11″ | 81001051

The Heckler & Koch MR556 A4 is a commercial MR/AR-style carbine built on H&K’s short-stroke gas piston architecture. This configuration reduces direct hot-gas fouling in the action and features an adjustable gas regulator for suppressed or unsuppressed use. The MR556 A4 retains fully ambidextrous controls and a slim M-LOK handguard to support modern accessories. Pair this platform with a compact red dot such as a Trijicon MRO for fast target acquisition under $1,000.

Common uses for this model include range training and competitive shooting or precision varmint work where a light, reliable piston-driven 5.56 platform is advantageous.

Product Specifications

• The caliber is .223 Rem/5.56 NATO.
• The barrel measures 11 inches and is threaded.
• The barrel type is Threaded.
• The action is Semi-Auto.
• The model designation is MR556 A4.
• The finish is Black Anodized.
• The handguard is M-LOK.
• The operating system is a short-stroke gas piston.
• The receiver is a fully ambidextrous lower.
• The firearm ships with no sights installed and is optics-ready.
• The package includes 1 10-round magazine.
• The NFA thread pattern is 1/2×28.
• The rate of twist is 1-in-7″.
• The additional features include HK416-style upper receiver.
• The UPC is 642230269446.

The MR556 A4 is engineered for shooters who prioritize durability and low maintenance in a 5.56 platform. Its piston system and adjustable gas regulator reduce fouling and allow tuning for suppressors, while the M-LOK handguard and ambidextrous controls provide a modern accessory footprint and ergonomic handling. This configuration suits range-focused users and competitors who want a proven, serviceable platform with modern ergonomics.

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