HK MR556 A4 11-inch AR Pistol, 5.56 NATO, Short-Stroke Piston, Ambidextrous Controls, Threaded 1/2x28
This factory 11-inch HK MR556 A4 AR pistol stands out for its short-stroke gas piston system with a two-position N/S adjustable gas block, a cold hammer forged match-grade barrel, and a fully ambidextrous control set. It features a slim free-float M-LOK handguard with a full-length T-marked Picatinny top rail, a 1:7 RH twist six-groove bore, and a 1/2x28 threaded muzzle with an open-prong flash hider. Overall condition is excellent.
Condition
Overall Condition: Excellent condition, showing only faint signs of any prior use or handling.
Bore Overall Condition: Excellent - Clean, mirror finish, no signs of wear.
Bore Rifling: Excellent Rifling - Sharp lands and grooves.
Proof Marks or Import Stamps: Heckler & Koch Inc., Columbus, GA.
Specific Condition Notes: There are superficial scratches and small blemishes from light handling.
What’s Included
- HK-branded soft case
- HK MR A4 Series operator's manual
- HK tool
- Assorted parts
- 1x 30-round Magpul PMAG GEN M2 MOE 5.56 polymer magazine
The MR556 A4 uses HK's proven short-stroke gas piston with a rotating bolt for clean, consistent operation. The two-position gas block is labeled N/S for normal or suppressed settings, allowing quick, positive adjustments at the block.
The 11-inch steel barrel is cold hammer forged and match grade with six-groove rifling and a 1:7 RH twist to stabilize common 5.56 NATO loads. It is threaded 1/2x28 and ships with an open-prong flash hider installed.
The lower is fully ambidextrous, including the bolt catch/release, magazine release, and a 45-degree throw selector. An ambidextrous charging handle with a large paddle offers positive manipulation. A forward assist, shell deflector, and dust cover are present.
The free-float slim aluminum M-LOK handguard includes QD sling sockets and a full-length, T-marked Picatinny top rail. No sights are installed, and the receiver uses a STANAG-compatible magazine interface with a 30+1 capacity.
This pistol configuration ships with a receiver extension installed and no stock or brace fitted. Frame and receiver components are aluminum alloy with an HK-pattern polymer pistol grip featuring molded texturing.