Description
The HK MR556 A4 5.56x45mm 11-inch Threaded Barrel is Heckler & Koch’s commercial evolution of the battle-proven HK416 platform, purpose-built for shooters who demand reliability in a compact package. This 11-inch configuration delivers the short-stroke gas piston system you trust, paired with an adjustable gas regulator and a threaded barrel for suppressor use. It’s a no-nonsense tool for duty, range, or field work, ready to run hard out of the box.
| Manufacturer | Heckler & Koch (H&K) |
|---|---|
| Model | MR556 A4 |
| Material | Steel barrel, aluminum handguard, polymer lower (per manufacturer specs) |
| Compatibility | .223 Rem / 5.56 NATO |
| Finish | Black anodized |
| Weight | Approx. 7.2 lbs (unloaded, per manufacturer specs) |
| Condition | New |
Key Features
- Short-Stroke Gas Piston System — Runs cleaner than direct impingement, keeps carbon out of the action, and cycles reliably in adverse conditions. Why it matters: less cleaning, more shooting, especially when suppressed.
- Adjustable Gas Regulator — Tune gas flow for suppressed or unsuppressed use. Why it matters: reduces recoil and bolt speed, extending parts life and improving follow-up shot speed.
- 11-Inch Threaded Barrel (1/2×28) — Compact enough for vehicle or close-quarters work, threaded for a suppressor or muzzle device. Why it matters: you get HK’s cold hammer-forged accuracy in a handy length.
- Fully Ambidextrous Controls — Ambidextrous bolt release, selector, and magazine release. Why it matters: lefties and righties both get a natural, fast interface without swapping parts.
- M-LOK Handguard — Slim profile with continuous top rail and M-LOK slots at 3, 6, and 9 o’clock. Why it matters: attach lights, grips, or lasers without adding bulk.
Who It’s For
This rifle is built for the southern shooter who values reliability over flash. Whether you’re running drills on the family farm, patrolling a property line, or hitting steel at the range, the MR556 A4 delivers HK’s proven piston performance. It’s also a natural fit for hunters who need a compact, suppressor-ready carbine for hogs or coyotes in thick cover. If you appreciate a firearm that works every time you pull the trigger, this one’s for you.
Pros & Cons
- Pro: Legendary HK piston reliability—runs dirty, wet, or dry.
- Pro: Cold hammer-forged barrel with a 1:7 twist stabilizes heavy 5.56 loads.
- Pro: Fully ambidextrous controls for left- or right-handed shooters.
- Con: Heavier than a direct-impingement carbine—around 7.2 lbs unloaded. That weight soaks up recoil but can feel hefty on long walks.
Comparison: HK MR556 A4 vs. Geissele Super Duty vs. LMT MARS-L
| Feature | HK MR556 A4 | Geissele Super Duty | LMT MARS-L |
|---|---|---|---|
| Operating System | Short-stroke gas piston | Direct impingement | Direct impingement |
| Barrel Length | 11 inches | 11.5 inches | 11.5 inches |
| Gas Adjustment | Yes, 4-position regulator | No (fixed gas block) | No (fixed gas block) |
| Ambidextrous Controls | Full (bolt release, selector, mag release) | Partial (selector only) | Full (bolt release, selector, mag release) |
| Weight (unloaded) | ~7.2 lbs | ~6.5 lbs | ~6.8 lbs |
| Price | $3,749 | ~$2,200 | ~$2,400 |
The HK MR556 A4 stands apart with its piston system and adjustable gas—ideal for suppressed use. The Geissele and LMT are lighter and cheaper, but neither offers the same piston reliability or gas tuning. If you shoot suppressed often, the HK is the clear choice.
FAQ
Does the MR556 A4 accept standard AR-15 magazines?
Yes, it uses any standard AR-15/M16 magazine, including Magpul PMAGs, Lancer L5s, and GI-style metal mags. No proprietary feed system here.
Can I mount a suppressor on the 11-inch barrel?
Absolutely. The barrel is threaded 1/2×28 and the adjustable gas regulator lets you tune for suppressed fire. Just make sure your suppressor is rated for 5.56 and barrel lengths under 11.5 inches.
Is the gas regulator user-adjustable without tools?
Yes, you can turn the regulator by hand or with a cartridge rim. Four settings: normal, adverse (for dirty/weak ammo), suppressed, and off (for single-shot or training). It’s simple and reliable.
What’s the twist rate on the barrel?
1:7 twist, cold hammer-forged. Stabilizes 55-grain to 77-grain bullets easily. Great for M193, M855, or match loads.
Why Buy from Us
- Nationwide delivery (all 50 states)
- Ships 1-2 business days
- 30-day returns
- Secure checkout
HK Rifles | Piston ARs | Suppressor-Ready Firearms
Last updated: April 2026
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