H&K MR556 A4 5.56x45mm 16.5in 10+1 Patriot Brown
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About this product
The H&K MR556 A4 is a semiautomatic AR-pattern rifle with a 16.5-inch barrel chambered in 5.56x45mm NATO that employs a short-stroke piston system for reduced fouling and enhanced reliability. Weighing 7.67 pounds with an overall length of 36.50 inches, it features ambidextrous controls, an adjustable gas regulator, and a 10+1 round capacity compliant with multiple state regulations. Its threaded muzzle and M-LOK handguard make it suppressor-ready and highly adaptable for tactical or precision applications.
What is the H&K MR556 A4 used for?
The H&K MR556 A4 is designed for duty, range training, and medium-range precision shooting where reliability and low maintenance are critical. Its piston-driven system reduces carbon buildup compared to direct impingement rifles, making it ideal for extended sessions without frequent cleaning. The adjustable gas block allows tuning for suppressed fire or varying ammunition types, while the 16.5-inch barrel balances velocity and maneuverability for practical engagement distances.
How does the H&K MR556 A4 compare to the Stevens 334 Rifle?
The MR556 A4 outperforms the Stevens 334 in rapid-fire scenarios and accessory compatibility, but the Stevens 334 in .308 Win offers superior long-range accuracy for bolt-action purists. Where the MR556 A4 provides semiautomatic functionality and a 10+1 capacity for dynamic shooting, the Stevens 334 achieves sub-MOA groups with match-grade ammunition at 600+ yards. For tactical use or high-round-count training, the MR556 A4's piston system and ambidextrous controls are decisive advantages.
What does it weigh and what are the dimensions?
The MR556 A4 weighs 7.67 pounds unloaded and measures 36.50 inches in overall length with a 16.50-inch cold hammer-forged barrel. Its 1:7 twist rate stabilizes heavier projectiles up to 77 grains effectively, and the hexagonal handguard provides 12 inches of continuous M-LOK mounting surface for lights, lasers, or grips. The six-position stock adjusts from 10.5 to 14 inches length of pull, accommodating shooters from 5'4" to 6'4" without modification.
Who is this NOT for?
This rifle is not for budget-conscious buyers or those seeking a lightweight hunting platform, given its $3,637.99 price tag and 7.67-pound weight. Hunters preferring minimal gear weight would better suit a Stevens 334 in .243 Win at nearly half the cost and 2 pounds lighter. Additionally, beginners unfamiliar with NFA regulations may find its threaded barrel and potential SBR configurations legally complex without guidance.
What's in the box?
The MR556 A4 includes one 10-round magazine, a operator's manual, and a HK factory test target showing 1.5 MOA grouping with M855 ammunition. Unlike some competitors, it does not include iron sights or a cleaning kit, requiring an additional $150-$300 investment for immediate zeroing. The Patriot Brown Cerakote finish is applied to the upper, lower, and handguard for consistent corrosion resistance.
Is the H&K MR556 A4 worth it at $3,637.99?
At $3,637.99, the MR556 A4 justifies its cost for professionals and enthusiasts who demand piston-driven reliability and regulatory compliance in restricted states. Compared to a $2,500 direct impingement AR-15, it offers 40% less gas system fouling and military-proven durability under adverse conditions. For shooters prioritizing low maintenance and suppressor readiness, the investment aligns with long-term performance and resale value.
Specs at a glance
Pros & cons
What works
- Short-stroke piston reduces carbon fouling by 40% compared to direct impingement AR-15s
- Ambidextrous controls include safety, bolt release, and magazine release for left-hand shooters
- Threaded 1/2x28 muzzle ready for suppressors without adapter
Trade-offs
- No iron sights included — adds $150-$250 for BUIS or optic
- 7.67 lb weight is 1.8 lb heavier than a comparable Daniel Defense DDM4V7
- 10-round magazine limit may require purchasing additional compliant mags for training
Key attributes
| upc | 642230271081 |
| manufacturer | Heckler & Koch / H&K |
| manufacturer part number | 81001204 |
| action | Semi-Auto |
| barrel length | 16.50" |
| caliber/gauge | .223 REM/5.56 NATO |
| capacity | 10 + 1 |
| safety | Ambidextrous Safety Lever |
Frequently asked questions
- Is it compatible with standard AR-15 magazines?
- Yes, the MR556 A4 accepts all STANAG 4179 pattern magazines, including Magpul PMAGs and HK steel magazines. However, it ships with a 10-round compliant magazine to adhere to state capacity laws. For full-capacity use, verify local regulations before purchasing 30-round options.
- Does it fit in a standard 36-inch rifle case?
- No, the 36.50-inch overall length requires a case with at least 37 inches of interior space for safe transport. I recommend Pelican 1750 cases or Savior Equipment's 42-inch double rifle bags for added protection and accessory storage.
- How long does shipping take to Montana?
- Shipping to Montana takes 7-10 business days via FedEx Ground with adult signature required. All firearms ship from our certified FFL in Phoenix, Arizona, and require verification with your local FFL before transfer.
- Can I return it if it doesn't cycle properly?
- Returns are accepted within 30 days for manufacturing defects, but cycling issues often resolve with gas regulator adjustment or ammunition change. HK's warranty covers parts and labor for 2 years, and we provide technical support for troubleshooting before initiating returns.