Gun Review: HK MR556A1

Alright so it is no secret that I am an H&K guy, and if you have followed my previous articles then you can definitely see that I have taken a liking to them over the years. Hell, the US Government will not let H&K import modern sporting rifles due to the ’89 import ban so I went out of my way to build a semi-automatic G36 clone out of an SL8 and even a title II UMP want-to-be out of a USC carbine. That being said, it came as a shock to me when I got selected to review the new H&K MR556A1. You see, the way us writers get selected to review products (when it comes to firearms) is done by rotation rather than intentional selection so I was thrilled when I got the word. I was also pleasantly surprised at how easy H&K was to deal with; I got in touch with a delightful H&K employee via e-mail and she had a shiny new MR556A1 rifle at my FFL within a week.

Now let me say this; I have damn near every H&K firearm that has ever been made available to non-SOTs in the USA but this is one gun even I thought I would never own. I figured it was just another piston driven AR variant with some bells and whistles and those wonderful two red letters than add a grand onto the price tag but I wanted to give the rifle the benefit of the doubt and try to put my pre-concieved notions aside to make this test as objective as possible. I am also not a big AR15 guy. I believe the platform is versatile and makes the most sense out of all the semi-auto .223 rifles out there to own due to parts availability, price, and a slew of other reasons but over the years I have quite simply grown bored with the platform. I have seven or eight of them sitting in my safe, but I honestly cannot remember the last time I have shot one of them. Regardless, I was still excited to hit the range with this new AR that is all the rage among special forces groups across the globe and is even slated to replace the M249 as a squad automatic weapon in some US military units (in a heavy barreled variant). So lets get to it.

In the box you get the rifle, an HK magazine (these are built like tanks), lock, manual, pin tool, multi tool, and some HK swag. The rifle comes equipped with the H&K diopter sights, which are a rotating drum and fixed front sight. So I loaded up my vehicle with the HK and some Privi Partisan 55 grain ammunition and got to it.


So after shooting a few shots I noticed that I was hitting several feet (not inches mind you) low. I went to my range bag to grab my handy-dandy H&K sight tool and noticed I did not have it on hand (d’oh). Oh well, that was not going to impede my progress. I took the ACOG off of my AUG and threw it on the MR556A1 to continue the accuracy test.


So I continued shooting sitting down with no rest or bags (I like shooting freehand) at 100 yards.


I shot five groups of five rounds like this and here is the best group:


And my worst:


So with PPU 55 grain ammo I averaged 1.26 inches at 100 yards. I am sure with bags or a rest I could have shot a consistent 1 inch group or better, but it doesn’t matter I suppose as this little accuracy test was acceptable. I spent the rest of the day shooting steel targets at 100 and 200 yards and shot six 30 round magazines for a total round count of 180. So accuracy is acceptable and I believe any AR15 worth its salt should be able to perform at least this well.

But how about reliability? Well, luckily every Saturday after the 4th of July I attend a local machine gun shoot (there is no better way to celebrate the independence of your country than by destroying a small part of it) and I got a chance to beat on this gun hard. I also corrected the sights and got the irons on target. So for a test of reliability I got twenty 30 round magazines (600 rounds) and fired them all back to back letting the gun rest only to hand off to other shooters. Mind you I told everyone to beat on it, rapid fire it, bump fire it, etc:




The HK chugged along and ejected each round perfectly and consistently to 3:00. The oil on the gas system burned off but that was the only smoking to note and the bolt carrier was reasonably cool to the touch (I had to verify that video where the HK rep fired a bunch of rounds on full auto then handed the bolt carrier off to someone else). So after this I had a well broken in HK MR556A1 and a pile of various spent magazines:


So it didn’t jam and I asked everyone who messed with it what they thought and if it felt any different than a DI AR15/M16. The general consensus was that the recoil impulse was unique and that it was comfortable to shoot, but nothing was super amazing or spectacular (I agree with what they said by the way). However a short 600 round torture test with no jams and minimal heat buildup was something I thought was pretty cool.

So it was time to clean the HK MR556A1. It is well known that piston guns run cleaner than a DI gun, but I wanted to see how much buildup there was. I put on a pair of new white inspection gloves (I keep a big bulk pack of them around for handling valuable firearms) to see how dirty the bolt and carrier got. I was shocked at the lack of buildup. First I had to use the tool located in the stock to open the gun up and pull the carrier:


I then prepared to wipe the carrier from the bolt to the back in one swipe with an inspection glove:


And this is all that was there after 780 rounds:


I must say that I was shocked. After a range outing with a 6920 or other DI AR variant the gun would be this dirty after a magazine or two.

So I thought I might use the rest of my glove to grab the carrier and wipe it all the way down:


After generously wiping the carrier down by hand my glove looked like this:


Nearly 800 rounds and that is all the glove showed, and gloves don’t lie (unless you are OJ Simpson I guess).

So the cleanliness of the carrier is a result of H&K’s short stroke AR18 derived gas system:


One thing I noticed is that the actual piston tappet is a G36/SL8 carry over, however the rest of the system is slightly different. I must say this system is quite astonishing and I have no complaints other than it adds weight to an already heavy rifle.


So there you have it, but now for my bullet points:

The Good:

  • As accurate as any other 16″ barreled AR variant I have played with
  • Very comfortable gun to shoot with a light recoil impulse, even for an AR
  • I like the diopter sights a lot, some may not
  • Cleaning this gun takes two or three patches and a bore snake
  • 780 rounds, no cleaning, no jams so the thing is reliable
  • Full length rail system and front quad rail
  • Tons of storage in the grip and stock
  • Upper and lower are incredibly tight
  • Flared magwell
  • Upper will fit other AR lowers

The Bad:

  • The rifle weighs 8.6 lbs
  • An HK sight tool is not included
  • The bore is not chrome lined (HK says for accuracy)
  • Will not suppress as well as a DI gun
  • Will not take pre-generation 3 p-mags
  • The bolt carrier is milled to prevent full auto function
  • The chamber has an odd extention to prevent the install of a 416 bolt
  • An RDIAS or Lightning link will not work (no fun switch for you) without serious work

The Ugly:

  • The MR556A1 rifle is priced at $3,295
  • $3,295 is a lot of money
  • $3,295 for an AR variant is just… damn (this coming from an HK guy)


So all in all for the price of $3,295 I would pass on the MR556A1. Yes, the rifle shoots well and is reliable, but unless you are a serious collector or just have to have what some consider the absolute best then pass on this gun and buy a much cheaper piston AR. If the price point was closer to $2,000 I would be a buyer but on popular auction sights these are going for $3,500 so obviously people are biting. IMO if you live in a free State then put that money towards a machine gun for investment purposes, and if you don’t then plop that cash down on your mortgage!

Alex C.

Alex is a Senior Writer for The Firearm Blog and Director of TFBTV.


  • floppyscience

    “The rifle weighs 8.6 lbs”

    I can never get over this. That’s a
    full 2lbs heavier than a comparable DI carbine. It damn well better be
    indestructible for all that extra weight.

    Good review though. As much as I like HK I can’t imagine dropping $3000+ on an AR that isn’t any more accurate than a $900 one.

    it seems HK was a little confused in the direction they were going with
    this rifle. They made a heavy, solid piston gun but forewent the chrome
    lined barrel for a little bit of extra accuracy. I think it’d have made
    more sense to chrome line the bore and play to the rifle’s strengths,
    which are reliability and durability.

    • Alex C.

      Thank you for the kind words, and I agree with everything you said my friend!

    • Something I find interesting are the views of some respected persons in the industry reference the chrome barrel lining.
      Many have said we don’t need chrome lining and I quote ” we’re not in a jungle”. Others have said once the chrome starts wearing which is long before the barrel is worn out, the accuracy goes to crap.
      Have any of you read similar opinions?

    • Suburban

      That barrel is thick under the handguards.

  • Nicholas Mew

    For that money I would rather get these reproduction German weapons. BD-42 Type G and BD44.

    • Nicholas Mew

      Or a Tigr with these stocks. After all I live in California.

    • Kyle Sarver

      Check out this tacticool BD44.

  • Not chrome lined… isn’t HK a fan of nitriding?

    • Rasheed W.

      Too expensive they said. They wanted to keep costs to a minimum so they could keep the rifle cheap for the customer.

  • insertjjs

    I think I’ll stick with my SIG 516. Even after adding an ACOG, I still payed over $1000 less than the MR556. That is a lot of money left over for ammo.

    • Rasheed W.

      Has the sig been reliable? A guy at the local gun shop here said they explode. But he also seemed like he might have been on drugs or a liberal.

      • insertjjs

        Only issue I have had was with some hard primers on some Tula ammo. otherwise it has been completely reliable. Your drug user/Liberal (same thing really) might have been thinking of the sig 556. I think there were some issues with those rifles in the past.

  • LJK

    “Will not suppress as well as a DI gun”

    Uh, why? I was under the impression that a gas piston desing is much easier to suppress than a DI gun since the extra gas pressure doesn’t affect the function of the rifle as much.

    • JumpIf NotZero

      I’m not sure who told the extra pressure does not effect the piston system because that is absolutely nonsense.

      The system is at higher pressure than the unsuppressed system. This causes the bolt to either or both unlock sooner or cycle faster. The bolt unlocks and starts moving backwards while the pressure is still high in the barrel. The gas/carbon/crap now has to low pressure areas to travel to, forwards out the muzzle and backwards down the barrel into the chamber. Suppressed piston guns GET AS DIRTY or dirtier when suppressed as DI guns. Sometimes dirtier because most piston guns are overgassed by default.

      It is complete fantasy that piston is “better” for suppressed. Equal at best. The real key to any suppressed system is being able to restrict gas enough to keep the cyclic rate LOWER when suppressed than unsuppressed. Most adjustable gas block systems do not go low enough IMO. But they are a good start.

      Fwiw, I think piston is a horrible idea when retrofit to the AR. HK is a more or less new design and not a retro. I still don’t think the benifits outweight the costs. If HK designed a DI gun I bet it would be 99% the same as their piston gun. For almost all AR owners, DI is the way to go.

      • Alex C.

        I agree that it is a fantasy that piston guns are better for suppressing. Believe me, I have thrown many a can on piston and DI guns and run the heck out of them on happy mode. Believe me, my FNC after 500 rounds suppressed on full auto is much easier to clean than an AR/M16 variant doing the same. In my experience though, DI guns are quieter than piston guns. Here you can see me running my FNC (can at the end). It is still quite loud. And yes I realize this is a long stroke gun:

      • Rasheed W.

        If DI is just as good as piston then why did our Tier 1 special forces switch to the HK416?

    • Alex C.

      In a DI gun the gasses slow down in the gas tube and more so when they slam into the carrier key and on into the bolt carrier (containing them for a bit inside the receiver). In a piston system such as the MR556A1’s, the gasses escape from the rifle almost immediately into the atmosphere traveling at a rate much faster than the speed of sound, creating more noise. Maybe I should get a decibel meter and test all sorts of platforms with my Gemtech G5?

  • Christoph Bücker

    The bolt carrier is milled to prevent full auto function
    The chamber has an odd extention to prevent the install of a 416 bolt

    The MR556 is the civilliant variant of the 416. Because of the german laws it isn´t just a converted rifle. It is a partially new development. A semi-auto weapon, according to german law must be designed that they can not be converted into a full-auto weapon, when the Semi-Auto weapon is a replica of a full-auto-weapon.
    Furthermore, the weapon must be designed so that it can not be converted to full automatic with common household tools.
    The last reason for the differences between 556 and 416 is a point in the German Weapons Act, which states that the civil weapon must be designed so that an installation of bolt, barrel and fire selector lever from a full-auto-weapon is not possible.

    • Alex C.

      The MR556a1 is made by HK USA here in America.

      • PR

        Designed in germany
        Partially manufactured in germany.
        I thought you were supposed to know what you were talking about.
        They do sell these to the German civilian market.

        • Alex C.

          The rifle for the European market is the MR223. Also, this rifle’s major components were made right here in Newington, New Hampshire. No more than 10 parts of a semi-automatic rifle may be made outside of the US, and no “non-sporting rifles” can be imported post-’89.

          • PR

            Yes, I know that.
            Anything that has German proofmarks is made in Germany, and subject to German laws.
            The only parts i’m aware of is the BCG.

        • Oh he does believe me!

  • claymore

    How did it ever get into our military’s hands if you can’t adjust the front sight post with a round tip?

    • Alex C.

      There is an optional flip up front sight that attached to the gas block. I have not seen one but I assume that it would be adjustable. Also due to the full length rail system you are free to add whatever sights you want.

  • Aaron E

    Alex I got to shoot the MR556A1 at the SHOT Show Media day, and the rifle at Media day shot very well. You did a great job explaining the good, the bad, and the ugly of this rifle. The after pictures do a remarkable job of pointing out the great benefit of a piston system over DI.

    The MR556A1 is a really nice rifle, but HK squarely placed the crown of royalty on themselves with price. Not a smart move if you’re seriously looking to make an impact on a market flooded with good alternatives. Expensiveness only goes so far to mark greatness!

    Your “worst” grouping had an obvious flyer, with 4 other shots in a much tighter group. In most shooting circles that flyer could easily be explained as shooter input, rather than rifle performance. Mention it, but a measurement of the smaller group would have been much more consistent with what you had in your other groupings. I’m confident that would have put the group average right at or below 1 MOA at 100 yards.

    • Alex C.

      Thank you Aaron. I agree that this rifle can out shoot me and that the performance could be improved if I had a rest or even some “good” ammunition (I should have tested multiple types and such, but I was more interested in reliability for this test). I have confidence that this is at least a 1 MOA gun. You are spot on with your cost analysis too!

  • hami

    Most of “the good” column is the upper receiver. Remember that HK sells the complete upper w/ buffer for around $1900.

    Still a lot of money but easier to swallow than $3200 for almost the same reliability and function. Especially if you already have a lower.

  • Rubble912

    While assigned the 416 (10.5 inch variant) I grew more and more impressed with it. From initial testing, to implementation and deploying with it, it exceeded all of my expectations. As noted, the recoil impulse is different, but in a good way. Combine this with the slower cyclic rate and heavier front end and the weapon is very controllable in full auto when compared to a DI M4.

    The weapon did not need gobs of lube (which attracts more particulate matter) to function as the round count increases and was unfailingly reliable.

    My two critiques are very minor. I HATED that grip, and I’m betting you will also. The exaggerated finger lip on the front of the grip will rub your hand raw on a long day of shooting. Second, those steel mags are improvements over aluminum GI mags…but not the end all be all. When training and performing mag changes with mags that are loaded and dropping them…the feed lips will bend just like any other mag. PMags and Lancer seem to take abuse better (and yes, that’s anecdotal).

    Thanks for a great review

  • Lance

    Its a cool rifle and be fun to have a civilian M-27. But NOT for the price for that you can get a Ruger SR-556 which is just as good has a better adjustable gas system and can take your Pmags. Not worth the money. PS can you get the rights to sell those Semi auto G-36s you built.

    PS dont forget H&Ks motto: Were H&K and you SUCK!!!

    • Lance lets drop the Were H&K and you suck. Damn it’s getting old not to mention incorrect.

    • Man pippy

      How about, “H&K: Too good for you” or “H&K: Cause your not worth it”

  • The Dizzle

    Thoughts on LWRC? As a HK fan myself, I wanted the MR556, but after the price and the non chrome lined barrel, I went with a LWRC M6A3. I’m very happy with that decision.

  • Doopington

    How’d you feel about the new HK rail sights? I wanted either HK’s or Centurion’s drum diopters, and if the C4’s are over $200 to begin with, even HK prices are getting attractive at that point…

  • TangledThorns

    Yeah, for that money you could get two LWRC M6A2s. I got mine for $1650 last year from CTD.

    • True but then it’s all in what you want. They still sell a bunch. In fact they are 6-8 months behind and they’re cranking them out.

    • Rasheed W.

      I remember when Cheaper Than Dirt were charging $150 for a non windowed PMAG and $3500 for a Colt 6920. They lost a large amount of their customer base permanently after that, hope it was worth it for them.

  • mw

    Isn’t this review a little (pronounced “years”) late?

  • Mazryonh

    You should have mentioned in the opening paragraphs that this is a civilian version of the HK416 rifle for 5.56mm NATO.

  • Shooter

    This weapon system replaced the m249 in USMC rifle platoons 2 years ago. I carried one for a year and it is a tremendous weapon IMHO when compared to the m16/m4 and the SAW. Much mor reliable, accurate, and easier to hold on target with the vicker sling that the Marines use with it.

  • Oso Pardo

    H&K hit hard the civilian market prices and for the military the cost overall the same as Colt or Bushmaster.

  • Bill

    Sound like more overpriced nonsense from H&K.