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

About this product

What is the H&K MR556 A4 5.56x45mm 11in Threaded Barrel rifle? It's a compact, piston-driven semiautomatic carbine purpose-built for suppressed Short-Barreled Rifle (SBR) applications under the NFA, delivering a 26.5-inch overall package at 6.61 pounds unloaded with a 10+1 capacity magazine configuration. This is not a direct-impingement AR-15; it's H&K's evolution of the HK416 platform for the civilian market, featuring an adjustable gas system and fully ambidextrous controls designed for duty-grade reliability in a compact form that demands a $200 tax stamp and Form 1 approval before you take possession.

What is the H&K MR556 A4 used for?

This carbine is engineered for SBR-specific roles where compactness and suppressor compatibility are legally permissible and tactically advantageous. It serves as an ideal platform for trained personnel in vehicle-based security details, as a compact patrol carbine for law enforcement where department policy allows, or for the serious civilian shooter who maintains a dedicated NFA trust for range and training use. The 11-inch barrel optimizes 5.56mm ballistics for close-quarters engagement distances up to 200 yards, while the robust piston system handles high-round-count drills without the carbon-fouling issues of a direct-gas system.

How does the H&K MR556 A4 compare to a similarly priced Daniel Defense MK18?

The MR556 A4 provides a superior gas piston operating system, while the Daniel Defense MK18 offers a more established aftermarket and lighter weight. Where the H&K's piston drive reduces receiver fouling by an estimated 70% compared to a direct-impingement system like the MK18's, the trade-off is a front-heavy balance and proprietary parts like the bolt carrier group. The MK18, at nearly a pound lighter, handles faster for transitions, but the MR556 A4 will run cleaner for longer during suppressed firing schedules, a critical factor if your main use case involves a can.

What does it weigh and what are the dimensions?

This carbine measures 26.5 inches from the end of the collapsed stock to the muzzle threads and weighs 6.61 pounds (107.4 oz) empty with no optic or magazine inserted. The 11-inch cold hammer-forged barrel features a 1/2x28 thread pitch, a standard for 5.56mm muzzle devices, and the 6-position stock collapses to reduce the overall length by approximately 5.5 inches for storage. For comparison, a traditional the 16-inch AR-15 like the Stevens 334 will be over 9 inches longer and often lighter due to its simpler gas system.

Who is this NOT for?

This is not a rifle for first-time buyers, budget-conscious shooters, or anyone unwilling to navigate National Firearms Act regulations. The $3,637.99 price tag is merely the entry fee; you must also budget for a $200 tax stamp, a Trust (recommended), a quality suppressor (adding $800-$1200+), and the 8-12 month waiting period for ATF approval. If your primary need is a straightforward, affordable rifle for general plinking or hunting, a standard 16-inch barrel model like the various Stevens 334 — our editorial take options represents a far more practical and legally simple choice.

What's in the box?

You receive the complete MR556 A4 rifle with one 10-round H&K proprietary steel magazine, a manual, and the factory case. Crucially, the box does not include any tools for adjusting the gas block, a thread protector (only the A2 flash hider is installed), or a sling. The rifle ships from the distributor configured for unsuppressed fire; you must manually dial the gas regulator to the suppressed setting using a flathead screwdriver or proprietary tool, a process that takes about 90 seconds once you understand the system.

Is the H&K MR556 A4 worth it at $3,637.99?

Yes, but only if your use case specifically demands a compact, suppressor-ready, piston-driven SBR from a manufacturer with proven military pedigree. You are paying a significant premium—often $1,500 more than a high-end DI-based SBR upper—for the HK416-derived operating system, the legendary H&K cold hammer-forged barrel, and the peace of mind from an over-engineered bolt and carrier. For the shooter who values extreme suppression reliability and reduced maintenance above all else in an NFA-controlled package, the cost is justifiable. For everyone else, it's an expensive lesson in diminishing returns.