HK MR556 A4 5.56 NATO Semi-Auto Rifle, 16.5 in Threaded Barrel, Short-Stroke Piston, M-LOK Handguard, Ambidextrous Controls
The MR556 A4 is Heckler & Koch's updated A4-series 5.56 NATO rifle, announced in late 2024 and configured with ambidextrous controls, a short-stroke gas piston system with a 2-position N/S adjustable regulator, and a 16.5 in threaded barrel. It features a slim free-float M-LOK handguard with a full-length T-numbered top rail, flip-up iron sights, and a matte black finish.
Condition
Overall Condition: Excellent condition, showing only faint signs of any prior use or handling.
Bore Condition: Excellent - Clean, mirror finish, no signs of wear.
Bore Rifling: Excellent Rifling - Sharp lands and grooves.
Specific Condition Notes: The exterior shows minor scratches and small blemishes from prior handling.
What's Included
- 1x 30rd Magpul PMAG Gen M3 polymer AR/M4 magazine
- Original case
- Straps for carry case
- Manual
- Toolset
HK pairs the MR556 A4 with a proven short-stroke piston operating system and a 2-position N/S adjustable gas regulator. The 16.5 in barrel is threaded at the muzzle and fitted with a birdcage flash hider. A 1:7 RH twist supports common 5.56mm NATO projectile weights.
The A4 generation brings ambidextrous controls, including the safety selector and magazine release, for straightforward manipulation from either side. A collapsible polymer stock and HK-pattern textured pistol grip provide a familiar AR-15 platform feel.
The free-float slim M-LOK aluminum handguard includes integral QD sling sockets and a full-length 12 o'clock Picatinny top rail with T-numbered reference marks. Flip-up front and rear iron sights come installed, and the receiver and components wear a matte black finish.
Details such as the HK MR-marked bolt carrier, factory markings "MR 556 A4 5.56 mm x 45," and proof/import stamps (Heckler & Koch Inc., Columbus, GA, HK over CE symbols) underscore the rifle's factory pedigree. Overall length spans 33.25–36.5 in, and weight is 7.67 lb.