The Heckler & Koch MR556 A4 Rifle (HK part no. 81001203) runs a short-stroke gas piston operating system instead of direct impingement, so hot carbon fouling never makes it back into the action. That means the rifle can run longer between cleanings with less wear on internal components, and an adjustable gas regulator lets the operator tune the action specifically for suppressed or unsuppressed use. Chambered in 5.56 NATO and also safe for .223 Remington, it’s built around a 16.5-inch threaded barrel with a fast 1:7 twist and finished in Patriot Brown over an M-LOK handguard. Fully ambidextrous controls, a lighter overall weight, and a slimmer profile than earlier HK carbines make the A4 easier to operate, manipulate, and employ.

Key Specifications

• Chambered in 5.56 NATO for reliable AR-15 performance.
• Also safely fires .223 Remington ammunition through the same chamber.
• Rifling twist rate of 1:7 suits heavier bullet weights.
• 16.5-inch threaded barrel accepts standard muzzle devices and suppressors.
• Ships with a 30-round magazine.
• Runs a short-stroke gas piston system with an adjustable regulator for suppressed or unsuppressed use.
• Fully ambidextrous controls make the rifle easy to operate from either side.
• Finished in Patriot Brown over the receiver.
• Equipped with an M-LOK handguard for mounting accessories.
• 6-position black synthetic stock allows length-of-pull adjustment.

Frequently Asked Questions

What operating system does this rifle use? A short-stroke gas piston system with an adjustable regulator for suppressed or unsuppressed operation.

What caliber does this rifle chamber? 5.56 NATO, also safe for .223 Remington.

Are the controls ambidextrous? Yes, the MR556 A4 features fully ambidextrous controls.

Buy the Heckler & Koch MR556 A4 Rifle

Want a gas-piston AR platform built for long service life? Order this Heckler & Koch rifle from our AR rifles lineup and we’ll ship it fast and insured to your local FFL from our Lubbock, Texas shop.