HK’s MR556A1, shown here with the SureFire M900A vertical foregrip…

HK’s MR556A1, shown here with the SureFire M900A vertical foregrip weapon light and an Aimpoint PRO with a 3XMag optic, features the same ultra-reliable gas piston system used by US Special Forces in the HK416, delivering premium performance in a patrol rifle.

Let’s face it, U.S. Special Operations units don’t scrimp on their equipment—nor do they stick with something if it doesn’t produce results. Given their use of and trust for Heckler & Koch (HK) firearms, it is not surprising that these units worked with that company in 2004 to develop the piston-driven AR carbine-style rifle that is known as the HK416.

The polymer dust cover on the MR556 is both quieter and impervious to corrosion while the captive takedown screw at the rear of the handguard makes its removal extremely easy.

The reputation this gun has earned among these elite warriors is due to its success in combat under the harshest conditions and its proven record of reliability, durability and accuracy. This, of course, almost immediately translated into a growing demand for a civilian version. Now, after many years of waiting, HK has introduced their MR556A1 rifle, which in many ways is an improvement over the military version.
I spoke with Wayne Weber, President of Heckler & Koch U.S.A. about the new rifle and he explained the difficulties that had to be overcome to offer a civilian version. This included dealing with subtle variations and improvements, to naming the new gun to the intricacies of US firearms import laws. Eventually all of these were resolved and the MR556A1 is now one of three HK firearms manufactured in the United States.

The rubber butt pad on the MR556 stock twists off to reveal an internal storage area for batteries and other equipment. This area also secures the disassembly tool.

Based on the standard M4-style rifle, and still chambered in 5.56x45mm, the new MR556 dispenses with the old gas impingement system of operation for a new, proprietary short-stroke gas piston system. Anyone familiar with the standard AR gas system knows that all the gasses, fouling and carbon from firing a round are directed back through the gas tube into the bolt and receiver to operate the rifle.

lent accuracy, but only so long as the gun is kept clean and well lubricated—and therein lies the rub. With gasses going back into the bolt and receiver, it not only heats up quickly, especially in full-auto, but also makes the most important moving parts very dirty. Indeed, cleaning an AR rifle is a chore that no one craves.

Load Comments
  • HK/Colt mongrel

    Presumably those optics were staged for the article.

    The Aimpoint red dot is not aligned with the 3x magnifier.

    LaRue produces QD mounts for Aimpoint optics, which align perfectly.

    Aimpoint also produces their own mount for the magnifier,

    which detaches completely when in a CQB situation.

    The LaRue version leaves the magnifier mounted but flips to one side.

  • Mike Chilton

    As a former Marine, and ret. Cop, X SWAT I love this gun, moving out of Calif and picking one up in Florida soon as I land there. From my research this is what Im getting for my M-4. Carried the HK MP5 and what a fine weapon on the teams. So I have no doubt about this weapon. I will pay the money!!!

  • Happy H&K owner

    I’ve been a proud owner of the MR556A1 for about a month now, and even having built many top quality AR’s for clients and myself, this is by far the most impressive rifle “out of the box” there is. Slap an optic on and you’re done. Unless you’re a iron sight type. Then you’re definately ready to go!! Don’t complain about the price tag. You’re getting a phenomenal product. Thanks H&K!!

  • Smitty

    I was actually one of the infantry guys chosen to field test the M27, which is similar to this weapon in build, and it was awesome. I was pleased to hear that the Marine Corps decided to purchase the M27. Too bad I got out a year ago. As far as this particular weapon goes, I’m actually thinking of buying one for my current job(military contracting, PSD/PST). If it performs as well, and I’m sure it does, as the M27, this would be money on the battlefield.

  • aaron

    as a former us marine i this is with out a doubt the best A1 on the market today!

    thank you h&k for another out standing weapon.