HK MR556 A4 | 5.56x45mm | 16.50 in | 30+1 | 81001203

The MR556 A4 is a semi-automatic 5.56x45mm rifle built around a short-stroke gas piston operating system that reduces hot carbon fouling in the action and lowers wear on internal components. It features an adjustable gas regulator for reliable function with suppressed or unsuppressed configurations, fully ambidextrous controls, and a slim profile designed for efficient handling. The Patriot Brown Picatinny rail receiver and M-LOK handguard offer mounting flexibility for accessories and optics. Pair this rifle with a Vortex Strike Eagle 1-6×24 for a durable, sub-$1000 optic that suits both close-to-mid range work and precision drills.

Product Specifications

• The manufacturer’s part number is HK 81001203.
• The caliber is .223 REM/5.56 NATO.
• The action is Semi-Auto.
• The capacity is 30 + 1.
• The barrel measures 16.50 inches and is threaded.
• The overall length is 36.50 inches.
• The weight is approximately 7.67 lbs.
• The rate of twist is 1:7.
• The rifle uses a short-stroke gas piston with an adjustable gas regulator for suppressed or unsuppressed operation.
• The safety is a Ambidextrous Safety Lever.
• The stock is a 6 Position black synthetic design.
• The receiver and major external finishes are Blued/Black with a Patriot Brown Picatinny rail.
• The hand orientation is Ambidextrous.
• The handguard is an M-LOK compatible design.
• The UPC is 642230271074.

Designed for shooters who prioritize reliability and low-maintenance operation, the MR556 A4 is well suited to range training and competitive rifle disciplines where consistent function and controllability matter. Its adjustable gas system and ambidextrous ergonomics make it adaptable to a variety of setups and user preferences. With a modular rail and M-LOK interface, the platform accommodates optics and accessories without sacrificing balance or muzzle-to-bore alignment.

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