The HK MR556 A4 is a semi-automatic AR-style pistol chambered in 5.56 NATO and built around HK’s short-stroke gas-piston operating system. Its 11-inch steel barrel has a 5/8x24 threaded muzzle, while the M-LOK handguard provides flexible accessory mounting. A Picatinny rail on the receiver supports the addition of an optic, and the ambidextrous safety lever accommodates right- and left-handed operation. The black polymer grip and six-position stock assembly complement the durable black finish. With a 10+1 capacity and an unloaded weight of 6.61 pounds, it offers a compact configuration for users seeking HK engineering in an AR-pattern platform.

Key features

• Short-stroke gas-piston system promotes reliable cycling and simplified maintenance
• 11-inch threaded barrel accepts compatible 5/8x24 muzzle devices
• M-LOK handguard supports flexible accessory placement
• Picatinny receiver rail is ready for a compatible optic
• Ambidextrous safety lever supports right- and left-handed handling
• 10+1 capacity provides practical ammunition capacity

The HK MR556 A4 combines a compact AR-pistol configuration with HK’s gas-piston operating system and robust accessory support.