The Heckler & Koch MR556 A4 is a semi-automatic rifle built around an HK416-style upper receiver and reliable short-stroke gas piston operating system. It features a 16.5-inch threaded barrel with a 1:7 twist, a fully ambidextrous lower receiver, HK416 Slimline furniture, and an M-LOK handguard. The collapsible stock provides an overall length of 33.25 to 36.5 inches. This black rifle accepts .223 Remington and 5.56 NATO ammunition and includes one 10-round magazine. Factory standard models do not include iron sights, allowing the user to select an optic or sighting system for the intended application.

Key features

• Short-stroke gas piston system supports dependable semi-automatic operation
• HK416-style upper receiver and fully ambidextrous lower receiver accommodate versatile handling
• 16.5-inch threaded barrel uses a 1/2x28 thread pattern and 1:7 twist
• M-LOK handguard provides flexible accessory mounting options
• Collapsible stock adjusts the overall length from 33.25 to 36.5 inches
• Optic-ready top rail allows installation of a compatible sighting system

The MR556 A4 combines HK416-derived operating features with an adaptable modern rifle configuration.