HK MR556A1 5.56 NATO Semi-Auto Rifle, 16.5 in CHF Heavy Barrel, Short-Stroke Piston, HK FFRS Quad-Rail, Threaded
The HK MR556A1 is a 5.56 NATO, AR-15–pattern rifle built around Heckler & Koch's short-stroke piston system derived from the HK416 program. This example features a 16.5-inch cold hammer forged heavy-profile barrel with a 1:7 twist and a threaded muzzle, an HK Free-Floating Rail System (FFRS) quad-rail with a continuous, position-numbered Picatinny top rail, and HK's E1 collapsible stock. It is assembled in the U.S. with American and German components, with the receiver marked Heckler & Koch Inc., Columbus GA.
Condition
Overall Condition: Very good condition, showing only light, superficial signs of prior handling or use.
Bore Overall Condition: Excellent - Clean, mirror finish, no signs of wear.
Bore Rifling: Excellent Rifling - Sharp lands and grooves.
Specific Condition Notes: There are minimal markings from previous handling and use. The bore is bright and clean. See photos for details.
What’s Included
- 2x 30-round magazines
- HK MR556A1 operator's manual
- HK-branded multi-tool
- Chamber flag/block (installed in magwell)
- HK small parts pack with hardware and hex key (bagged)
The MR556A1 uses HK's proven short-stroke piston pusher-rod operating system. The design traces directly to the HK416 program and includes an HK-marked bolt, forward assist, case deflector, and an ejection-port dust cover.
The 16.5-inch steel barrel is cold hammer forged, heavy profile, and non-chrome-lined, with a 1:7 twist to stabilize a wide range of 5.56mm projectiles. The muzzle is threaded.
The HK Free-Floating Rail System (FFRS) is a quad-rail that returns to zero and includes a continuous, position-numbered Picatinny top rail. The rifle ships without sights, allowing the buyer to configure as needed.
Controls and furniture include a two-stage trigger, ambidextrous manual safety, and the HK E1 collapsible stock with six positions, adjustable length of pull, and a rear sling loop. The aluminum receiver and frame wear a matte black hard-coat anodized finish.
This rifle is assembled in the USA using American and German components. The receiver is marked Heckler & Koch Inc., Columbus GA. Capacity is 30+1 with standard AR-pattern magazines.