H&K MR556 A4 5.56x45mm 11in Threaded Barrel 10+1

Description

The Heckler & Koch MR556 A4 5.56x45mm 11in Threaded Barrel 10+1 is a compact piston-driven carbine built for shooters who demand reliability in tight quarters. Chambered in .223 Rem/5.56 NATO, this model pairs an 11-inch cold hammer-forged barrel with a short-stroke gas piston system that cuts carbon fouling and keeps your action running clean. At $3637.77, it’s a serious investment—one that delivers proven HK engineering in a slimmer, ambidextrous package.

Manufacturer	Heckler & Koch
Model	MR556 A4
Material	Cold hammer-forged barrel, aluminum upper/lower receiver (per manufacturer specs)
Compatibility	.223 Rem / 5.56 NATO
Finish	Hard-coat anodized black
Weight	Approx. 7.2 lbs (unloaded, per manufacturer specs)
Condition	New

Key Features

• Short-Stroke Gas Piston System – Why it matters: Reduces carbon buildup inside the receiver, meaning less cleaning and longer life between maintenance cycles compared to DI guns.
• Adjustable Gas Regulator – Why it matters: Switch between suppressed and unsuppressed settings without swapping parts—keeps the gun cycling reliably with a can attached.
• Fully Ambidextrous Controls – Why it matters: Lefties and righties get equal access to the bolt release, magazine release, and safety selector, no aftermarket parts needed.
• 11-Inch Threaded Barrel (1/2×28) – Why it matters: Compact enough for vehicle or home defense use, and the threads let you mount a suppressor or muzzle device right out of the box.
• Slimmer Profile Handguard – Why it matters: Easier grip for smaller hands and better control during rapid fire, plus M-Lok slots for lights or lasers.

Who It’s For

This carbine fits three types of shooters: the home defender who wants a compact, reliable platform; the suppressor enthusiast who needs an adjustable gas system; and the HK loyalist who appreciates the brand’s cold hammer-forged barrels and piston reliability. If you run classes or drills in tight spaces, the 11-inch barrel keeps you maneuverable without giving up 5.56 terminal performance.

Pros & Cons

• Pros: Piston system runs cleaner than DI; fully ambidextrous out of the box; adjustable gas regulator works with suppressors; HK cold hammer-forged barrel accuracy.
• Cons: The price point is steep compared to DI ARs; the 10+1 magazine capacity may feel limiting in states with standard-capacity options (check local laws).

Comparison: MR556 A4 vs. Geissele Super Duty vs. Zev Technologies AR

Feature	HK MR556 A4	Geissele Super Duty	Zev Technologies AR
Operating System	Short-stroke gas piston	Direct impingement	Direct impingement
Barrel Length	11 inches	14.5 inches	10.5 inches
Gas Adjustment	Adjustable regulator	Fixed (suppressor-ready with gas block)	Fixed
Ambidextrous Controls	Full ambi (bolt, mag, safety)	Ambi safety only	Ambi safety and mag release
Price	$3,637.77	$1,800–$2,200	$1,500–$2,000

The HK MR556 A4 stands out for its piston reliability and full ambidexterity, but you pay a premium. The Geissele Super Duty is a proven DI gun with a longer barrel and lower price, while the Zev offers a shorter barrel but lacks the piston system and gas adjustability.

FAQ

Is the barrel compatible with standard AR-15 suppressors?

Yes. The 11-inch barrel is threaded 1/2×28, which matches most 5.56 suppressors. Use the adjustable gas regulator to tune for suppressed fire.

Can I use standard AR-15 magazines with this carbine?

Yes. The MR556 A4 accepts all standard AR-15/M16-pattern magazines. It ships with one 10-round magazine.

Does this model have a chrome-lined barrel?

No. The cold hammer-forged barrel is not chrome-lined, but HK’s proprietary surface treatment provides corrosion resistance and extended barrel life per manufacturer specs.

What is the twist rate on the 11-inch barrel?

1:7 twist rate, optimized for 55–77 grain 5.56 loads.

Is the handguard compatible with M-Lok accessories?

Yes. The slim handguard features M-Lok slots at the 3, 6, and 9 o’clock positions.

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Explore more: Semi Auto Handguns | AR-15 Parts | Suppressors

Last updated: April 2026

According to industry data, piston-driven ARs account for roughly 12% of the aftermarket rifle market, with HK holding a significant share among premium brands.