HK MR556 A4 11-inch 5.56mm NATO AR Pistol, Short-Stroke Piston, CHF Match Barrel, M-LOK
This Heckler & Koch MR556 A4 pistol pairs HK's proven short-stroke gas piston system with an 11-inch cold-hammer-forged match barrel and a slim free-float M-LOK handguard. It features a 2-position adjustable gas regulator, a continuous T-marked Picatinny top rail, and an ambidextrous dual-latch charging handle. Overall condition is excellent, with only faint signs of prior handling.
Condition
Overall Condition: Excellent condition, showing only faint signs of any prior use or handling.
Specific Condition Notes: There are some superficial scratches and blemishes present on exterior surfaces.
Bore Overall Condition: Excellent - Clean, mirror finish, no signs of wear.
Bore Rifling: Excellent Rifling - Sharp lands and grooves.
What’s Included
- HK-branded soft carry case
- 1x 30rd Magpul PMAG polymer magazine with window
The MR556 A4 operating system uses a short-stroke gas piston with a 2-position (N/S) adjustable regulator. This design vents fouling away from the receiver and is built for consistent function across a range of conditions and ammunition types.
The 11-inch steel barrel is cold-hammer-forged and match-grade, threaded 1/2x28, and fitted with an A2-style flash hider. A 1:7 RH twist supports modern 5.56mm NATO projectile weights, and the free-float design helps maintain barrel harmonics.
The slim aluminum M-LOK handguard reduces bulk while providing direct accessory mounting, plus integrated QD sling sockets. A continuous T-marked Picatinny top rail runs from receiver through the handguard for uninterrupted alignment. Controls include an ambidextrous dual-latch charging handle, forward assist, ejection-port cover, and a manual safety selector.
Receivers are aluminum alloy with a pistol receiver extension and end cap (no stock/brace). Factory-listed overall length is approximately 26.5 inches and weight is approximately 6.61 pounds. Capacity is 30+1 with the included 30-round PMAG. Markings include the HK logo, MR 556 A4 5.56 mm x 45, and Heckler & Koch Inc., Columbus, GA.