HK MR556 A4 5.56mm NATO Semi-Auto Rifle, 16.5-inch CHF Match Barrel, Short-Stroke Piston, Fully Ambidextrous Controls
The HK MR556 A4 is the civilian counterpart to the HK416 family, built in the United States and configured as part of the MR A4 Series. This rifle combines a 16.5-inch cold hammer forged match barrel in cannon-grade steel with a proven short-stroke gas piston system and fully ambidextrous controls. A slim free-float M-LOK handguard with a continuous T-marked top rail, an HK416-style adjustable stock, and an HK-pattern grip round out a feature set focused on durability and precise function.
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: There are superficial scratches and small blemishes consistent with prior use. The rifle shows evidence of previous firing but was maintained very well. The bore is clean and shiny.
What’s Included
- HK soft rifle case with logo
- Case organizers
- HK MR A4 Series operator's manual
- Cable lock
- Two 30-round magazines:
- One HK-marked aluminum AR-15 magazine with "RESTRICTED LAW ENFORCEMENT / GOVERNMENT USE ONLY 10-94" stamping
- One polymer AR-15 magazine with a side witness window
The MR556 A4 uses a gas-operated short-stroke piston with a rotating bolt and a two-position adjustable gas regulator for suppressed or unsuppressed use. This setup is engineered for consistent cycling and clean operation across a wide range of 5.56mm NATO loads.
Its 16.5-inch match, cold hammer forged barrel is made from cannon-grade steel with 6-groove rifling and a 1:7 right-hand twist. The barrel is threaded 1/2x28 UNEF and fitted with a birdcage flash hider, offering a durable, ready-to-use muzzle interface.
The slim, free-float M-LOK handguard integrates a continuous T-marked top Picatinny rail (numbers 2–30 visible), providing a rigid mounting surface along the full length of the upper while keeping weight and bulk in check.
Controls are fully ambidextrous, including the bolt catch/release and magazine release, paired with an ambidextrous safety featuring a 45-degree selector. An ambidextrous, extended charging handle with dual latches enhances manipulation from either side.
Furniture includes the HK416-style slimline, 6-position collapsible stock for adjustable length of pull and an HK-pattern pistol grip with molded HK logos. The aluminum-alloy receivers include an ejection-port cover marked "HK MR," and the upper shows the HK CE compliance mark.