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Something to make clear from the get go, the MR556A1 is outfitted with the same ultra-reliable gas piston system used in the HK416 that is standard among U.S. Special Forces, mainly the elite Navy SEALS. And to state the obvious, U.S. Special Operations units are not frugal when it comes to their equipment nor do they stick with something if it doesn’t produce high performing results.

Essentially, the MR556A1 is the civilian version of the world famous HK416. HK cut no corners in developing the MR556A1 for the commercial market, making Swiss-watch quality their bottom line, rather than cheap out on materials and manufacturing processes.



Externally, the MR556A1 resembles the AR-15/M-16 platform, but internally is where it significantly differs. Instead of utilizing the AR-15/M16’s direct impingement system, where combustion gases directly act upon the rifle's bolt, the MR556A1 relies upon a short-stroke gas piston similar to that found in the HK G36.

Now where does the improvement lie? The AR-15/M16’s direct impingement system major flaw is that it lets combustion gases into the internals of the weapon. This causes higher levels of fouling and results in more issues that can lead to a slew of more problems from jamming to shorter life spans. On the other hand, the MR556A1, using the above mentioned short-stroke gas piston system, drives an operating rod to force the bolt carrier to the rear preventing propellant gases from entering the internals.

The results are tremendous. The MR556A1 runs cooler, cleaner and more reliably and when adverse conditions, like dust, sand and mud are introduced,the advantage of the HK system becomes even more drastic. In fact, during factory tests the HK416 was able to fire 10,000 rounds in full-auto without malfunctioning a single time.

Onto the rest, the MR556A1 is also outfitted with a a proprietary accessory rail forearm that comes with MIL-STD-1913 rails on all four sides. This allows the user to equip their MR556A1 with most current accessories made for M4/M16-type weapons. In addition, the rail forearm is "free-floating" and does not contact the barrel, improving accuracy.

Another flagship feature of the MR556A1 that many civilians love is the fact that you can attach any M16/M4/AR-15 family lower receiver to the MR556A1 upper receiver since the take-down pins are located in the same standard position.

The MR556A1’s barrel is cold hammer forged from the highest quality cannon-grade steel. It has a 1 in 7” twist and a taper-bore configuration, with a slightly smaller diameter at the muzzle for improved accuracy and velocity. And while the material and cold hammer forging process themselves greatly enhance durability, HK’s processes includes several additional steps not taken by other manufacturers in order to produce superior accuracy and service life, ensuring performance well beyond “mil-spec.”


Browse our extensive collection of HK firearms from the ultra-reliable VP9 to the highly sought MR556A1 in FDE!


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