H&K MR556 A4 5.56 11in Threaded Barrel M-LOK

The Heckler & Koch MR556 A4 is a compact AR-pattern firearm built around HK's short-stroke gas piston operating system. It is fitted with an 11-inch threaded barrel and a slim M-LOK handguard, and it features fully ambidextrous controls for ergonomic operation. The platform is configured to be optics-ready and to accommodate suppressed or unsuppressed use via an adjustable gas regulator.

Key Specifications

• The model is MR556 A4.
• The caliber is .223 REM / 5.56 NATO.
• The barrel measures 11 inches and is threaded with a 1/2x28 pattern.
• The operating system is a short-stroke gas piston.
• The handguard uses M-LOK attachment points.
• The receiver features a fully ambidextrous lower for control access on both sides.
• The overall length is 26.50 inches.
• The weight is 6.61 lbs.
• The rate of twist is 1-in-7".
• The controls include an ambidextrous safety lever and an HK enhanced ergonomic polymer grip.

Engineered for reliability and reduced maintenance, the MR556 A4 combines HK's piston-driven reliability with a compact, serviceable AR-pattern layout. Its threaded barrel, optics-ready receiver, and ambidextrous ergonomics make it a practical choice for range-focused shooters and professionals who value a durable, precision-capable platform.