HK MR556A1 5.56 NATO Semi-Auto Rifle, Short-Stroke Piston, 16.5 in Threaded Barrel, Free-Float M-LOK Handguard, HK E1 Stock, Ambi Controls, Custom Ambi Charging Handle
The HK MR556A1 is a U.S.-made, AR-15 platform rifle built around Heckler & Koch's short-stroke gas piston system. This example stands out with a custom ambidextrous extended-latch charging handle engraved with "DON'T TREAD ON ME," an HK E1 collapsible stock, and an aluminum free-float M-LOK handguard with a full-length T-marked Picatinny rail. It retains HK factory touches such as an MR-marked bolt carrier, "CD" factory code stamps, and ambidextrous selector with HK pictogram markings.
Condition
Overall Condition: Good condition, showing some signs of prior use and handling.
Bore Condition: Excellent - Clean, mirror finish, no signs of wear.
Bore Rifling: Excellent Rifling - Sharp lands and grooves.
Specific Condition Notes: Expect visible handling marks from prior use. Please refer to the photos for a close look at external wear and markings.
What's Included
- Ambidextrous charging handle with "DON'T TREAD ON ME" engraving (installed)
- Magpul pistol grip (installed)
- One 30-round Amend2 polymer magazine
The MR556A1 uses HK's semi-automatic, short-stroke gas piston action, paired with an MR-marked bolt carrier. This operating system is designed to run cooler and cleaner than traditional DI systems, and it is a defining feature of the MR-series rifles.
The 16.5 in medium/heavy, free-floated barrel is threaded and set under an aluminum free-float M-LOK handguard. A full-length, T-marked 12 o'clock Picatinny rail spans the upper and handguard, and the rifle includes a forward assist and ejection-port dust cover. No sights are included.
Controls and ergonomics are well-appointed: an ambidextrous safety selector with HK pictogram markings and a custom ambidextrous extended-latch charging handle enhance handling for either hand. A Magpul pistol grip is installed for a modern, secure interface.
Furniture includes the HK E1 collapsible stock with a thick ribbed rubber buttpad and integral sling slot. The receiver wears a matte black hardcoat finish, and factory "CD" code stamps appear on the upper and handguard. It accepts detachable STANAG magazines and ships with one 30-round Amend2 magazine.