HK MR556 A4 | 81001204 | 5.56x45mm | 16.50″

The MR556 A4 is a semi-automatic piston-driven AR-pattern rifle designed for extended reliability and reduced fouling in the action. Its short-stroke gas piston system and adjustable gas regulator let the operator tune the rifle for suppressed or unsuppressed use while minimizing wear on internal components. The rifle is fully ambidextrous and features a slim, lighter profile for easier handling and manipulation. Pair this platform with a Vortex Strike Eagle 1-8×24 for a durable, versatile optic under $1000 that complements both close-to-medium range work and precision-oriented shooting.

Product Specifications

• The caliber is .223 REM/5.56 NATO.
• The action is Semi-Auto.
• The barrel description is Threaded.
• The barrel length is 16.50″.
• The barrel length range is 16″ to 16.99″.
• The capacity is 10 + 1.
• The weight is 7.67 lbs.
• The weight range is 7 lbs to 7.99 lbs.
• The handedness is Ambidextrous.
• The finish style is Blued/Black.
• The overall length is 36.50″.
• The safety is Ambidextrous Safety Lever.
• The stock description is 6 Position.
• The stock finish group is Black.
• The rate of twist is 1:7″.
• The UPC is 642230271081.

This MR556 A4 balances a durable short-stroke piston system with modern ergonomics and an M-LOK handguard for accessory flexibility. Its ambidextrous controls and adjustable gas system make it suited to extended-range training, precision-oriented competition formats, and disciplined field use where reliability and low maintenance are priorities. The platform’s slim profile and six-position stock help tailor fit and handling for a wide range of shooters.