The Heckler & Koch MR556 A4 (part no. 81001313) is a 5.56 NATO AR pistol built to the same exacting standards HK is known for on its full-size rifles, scaled down to an 11-inch-barrel pistol format. It’s a semi-automatic platform designed for shooters who want HK-level fit, finish, and reliability in a compact, maneuverable package suited to home defense or close-range work.

Key Specifications

• Features an 11-inch barrel.
• Uses a 1-in-7 twist rate.
• Chambered in .223 Rem/5.56 NATO, the standard AR-platform caliber.
• Ships with a 10-round magazine for 10+1 total capacity.
• Ships with no sights installed, keeping the top rail clear for an optic.
• Runs a semi-automatic action on HK’s proven platform.
• Ships at approximately 11.2 pounds.
• Measures 12.8 inches wide by 4 inches tall in its shipping package.
• Operates on HK’s proprietary short-stroke gas piston system, derived from the HK416, for cleaner and more reliable cycling than a direct-impingement design.

Frequently Asked Questions

What caliber is the MR556 A4 chambered in? .223 Rem/5.56 NATO.

What is the twist rate? 1-in-7, suited to a wide range of 5.56 bullet weights.

Does it come with sights? No, it ships optic-ready with no sights installed.

Buy the Heckler & Koch MR556 A4 Pistol

Built to HK’s exacting standards, the Heckler & Koch MR556 A4 is a standout in our AR pistols lineup. Order it from our Lubbock, Texas gun shop for fast, insured shipping to your FFL.