HK MR556 A4 | 5.56 NATO | 16.5in | 10+1 | 81001033

The HK MR556 A4 is a semi-automatic rifle built around a short-stroke gas piston system that reduces carbon fouling in the action and lowers maintenance compared with direct-impingement designs. The A4 features a threaded barrel, fully ambidextrous controls, and an adjustable gas regulator for tuning suppressed or unsuppressed operation. The rifle ships in a California-compliant configuration and includes one 10-round magazine.

For optics, a versatile choice under $1,000 that pairs well with this platform is the Vortex Strike Eagle 1-6×24, which offers a low-power variable magnification range suitable for both close and intermediate distances.

Applications: range training and tactical/practical shooting.

Product Specifications

• The manufacturer is Heckler & Koch / H&K.
• The model is MR556 A4.
• The manufacturer’s part number is 81001033.
• The caliber is .223 Rem / 5.56 NATO.
• The capacity is 10 + 1.
• The barrel length is 16.5 inches.
• The action is Semi-Auto.
• The operating system uses a short-stroke gas piston and includes an adjustable gas regulator.
• The rate of twist is 1:7.
• The NFA thread pattern is 1/2×28.
• The weight is 7.67 lbs.
• The overall length is 33.25 to 36.5 inches.
• The stock finish is Black.
• The rifle is configured for Ambidextrous operation (controls and receiver).
• The UPC is 642230269422.

The MR556 A4 delivers a robust, low-maintenance operating system with user-friendly controls and accessories that suit extended range sessions and tactical-style training. Its threaded barrel and adjustable gas system add adaptability for a variety of setups while the HK416-style furniture and M-LOK handguard make it straightforward to mount accessories and configure ergonomics. This is a deliberate choice for shooters who prioritize long-term reliability, straightforward maintenance, and modularity in a semi-automatic rifle platform.