HK MR556 A4 5.56 NATO Semi-Auto Rifle, 16.5 in Cold Hammer Forged Threaded Barrel, Short-Stroke Piston, Ambidextrous Controls
This MR556 A4 is part of HK's MR A4 series refresh derived from HK416 technology. It features a 16.5 in cold hammer forged, threaded barrel with a 1:7 twist, an adjustable Normal/Suppressed gas block, and fully ambidextrous controls. The rifle is in excellent condition and includes one 30-round PMAG, an HK-branded soft case, and the HK MR556 A4 operator's manual.
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: Exhibits minimal evidence of prior use. The bore has a bright, mirror-like interior.
What's Included
- HK MR556 A4 5.56 NATO semi-auto rifle
- 1x 30-round Magpul PMAG GEN M3 magazine
- HK-branded soft rifle case
- HK MR556 A4 operator's manual
Built on an AR-15 platform and informed by HK416 technology, the MR556 A4 uses a semi-automatic, short-stroke gas piston system with a rotating bolt. The adjustable gas block offers Normal/Suppressed settings, supporting reliable function across different use conditions. A case deflector and an ejection-port cover are fitted.
The 16.5 in steel barrel is cold hammer forged with a 1:7 right-hand twist and 6-groove rifling. It is threaded 1/2x28 and capped with an A2-style birdcage flash hider. This configuration provides broad compatibility with standard 5.56 mm muzzle devices.
Controls are fully ambidextrous, including the bolt catch/release, magazine release, and charging handle. An ambidextrous safety selector and a two-stage trigger round out the fire-control features. The slim, six-position collapsible stock provides a 14.0 in length of pull.
The free-float slim HK M-LOK handguard integrates with a full-length, numbered Picatinny top rail that bridges the receiver and handguard. No sights are installed, leaving the top rail unobstructed for user-selected sighting systems. Receiver roll marks include "MR 556 A4 5.56 mm x 45" with HK pictogram selector marks, and the rifle bears Heckler & Koch Inc., Columbus, GA import markings. Overall length is approximately 33.25-36.5 in and weight is approximately 7.67 lb. Capacity is 30+1.