H&K MR556 A4 | 5.56 NATO | 16.5″ | 30+1

The HECKLER AND KOCH (HK USA) MR556 A4 is a semi-automatic rifle built on HK416-style components and finished in gray Cerakote. It is chambered for .223 REM/5.56 NATO with a 16.5 inch threaded barrel and a 30+1 capacity magazine. The MR556 A4 uses a short-stroke gas piston system and an HK416 slimline collapsible stock and furniture for reliable operation and user ergonomics. For optics, this platform pairs well with a Vortex Viper PST Gen II 1-6×24 or an Aimpoint PRO, both of which are available for under $1000 and suit close-to-mid-range work on an AR-style rifle.

Applications for this rifle include precision-focused range training and action-style competition where a piston-driven AR offers consistent performance and reduced direct impingement fouling.

Product Specifications

• The manufacturer is HECKLER & KOCH INC..
• The ATF model designation is MR 556 A4.
• Chambered in .223 REM/5.56 NATO.
• The action is Semi-Auto.
• The barrel measures 16.5 inches and is threaded.
• The magazine capacity is 30 + 1.
• The overall weight is 7.67 lbs..
• The finish is Gray Cerakote.
• The furniture is HK416 Slimline with a collapsible/folding stock.
• The handguard features M-LOK attachment points.
• The lower receiver is fully ambidextrous.
• The rifling twist rate is 1-in-7″.
• The barrel thread pattern is 1/2×28.
• Factory configuration includes 1 30 rd. magazine.
• The overall length adjusts from 33.25 to 36.5 inches.
• The UPC is 642230271982.

With its piston-driven HK416 upper, slimline furniture and versatile 16.5″ threaded barrel, the MR556 A4 is built for shooters who want reduced maintenance and consistent performance across extended sessions. The rifle’s combination of proven ergonomics, modern M-LOK modularity and a robust ambidextrous lower makes it a logical choice for disciplined range work or competitive environments where reliability and controllability matter.