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Heckler & Koch MR556A1 Review: A Tank of an AR-15 preview image
Aug 03 2023
7 min read

Heckler & Koch MR556A1 Review: A Tank of an AR-15


Heckler & Koch (HK) is known for its high-quality and reliable firearms. The MR556A1 is no different and, as such, has become quite popular.

Being a direct descendant of the well-known HK416, it’s made with many of the same parts, including HK’s proprietary short-stroke gas piston system. It’s essentially the civilian version of the HK416 and is actually assembled in the beautiful US of A.

The MR556A1 falls into a price category I don’t usually shop in for an AR-15, so I haven’t sought one out to test before. However, when I had the opportunity to shoot one at Industry Day at the Range this year, I didn’t pass it up.

hk mr556 review at industry day at the range shot show
The MR556A1 is assembled in the USA using US and German parts.

By the end of the article, I hope you’ll be able to decide for yourself if it’s worth the steep price tag. Enjoy!

HK MR556A1 Review

HK MR556A1 For Sale

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Operating SystemShort Stroke Gas Piston
Barrel Length16.5 Inches
Overall Length33.9 – 37.7 Inches
Width3.1 Inches
Height9.5 Inches
Weight8.6 Pounds w/out Magazine
Trigger Pull7.6 Pounds
Sight Radius14.6 Inches

Pros & Cons

  • Exceptionally accurate and reliable
  • Short-stroke gas piston system
  • Enhanced internals
  • Longevity – built to last
  • Expensive – you’ll need some deep pockets
  • Picky with magazines (from what I’ve read, not experience)
  • Proprietary parts
  • Heavier than average AR

Time for the Range

Reliability & Accuracy

Reliability is not something you’ll need to be concerned about with the MR556A1. There is a reason that various military and special forces all around the world have been known to use, and continue to use it (HK416 version).

Through my own time shooting it, I had zero issues. It ran extremely smoothly, even after it had been shooting non-stop, all day long.

The exact unit I was shooting had an Aimpoint Duty RDS mounted on it, which made ringing the steel targets between 25 and 100 yards easier than falling off a log. The rifle would definitely out-shoot me, and I would love to see how it would perform in the hands of a sharpshooter or true operator.

Overall Feel

It feels like you’re driving a tank among Honda Civics. It looks like a standard AR, but it’s heavier and feels really sturdy right off the bat. Coming in at 8.6 pounds without a magazine, once you load the metal magazine with 30 rounds…you get the idea.

hk mr556 review at industry day at the range shot show
Looks can be deceiving. The MR556A1 looks standard but definitely doesn’t feel standard in hand.


Proprietary Piston Operating System

One of the main driving factors of the reliability of the MR556A1 is HK’s proprietary short-stroke gas piston system. In short, compared to a direct impingement system, it prevents the exhaust gasses from entering and fouling up the upper receiver.

This results in a rifle that runs cleaner, cooler, and more reliably. Keep in mind, though, this usually will increase the cost and weight of the gun.  

Rail System

The free-floating handguard is very smooth and comfortable, and is literally covered in M-Lok slots. Up top, the rail runs the entire length of the receiver and handguard, giving you plenty of room to mount some backup sights and your favorite optic.

hk mr556 review barrel rail m-lok
I hope you like M-Lok accessories because you have room to mount a ton of them.


The star of the furniture has to be the buttstock.

It has a nice-sized cheek weld, the buttpad does a great job at further minimizing felt recoil, and there is a ton of internal storage room for some spare batteries, rounds, or tools.

My one complaint though, is that it does not have any QD mounting points, only sling loops.

hk mr556 review stock
That’s a nice butt…stock! It was one of the more comfortable ones I’ve tried lately.

I was surprised to see a Magpul MOE grip at this price point, but it’s at least better than your standard A2 style. The grip also has internal storage, so between the buttstock and the grip, you’ll have ample storage room.

Controls & Trigger

Taking a look at the controls and trigger, I’m left with a mixed bag of emotions. Let’s start with the trigger.

The trigger pull is said to weigh in right around 7.6 pounds, and let me say, it definitely feels like it. While a heavier pull isn’t the worst thing in the world, I would have loved a lighter trigger on this rifle. The trigger guard also was a let-down, as it seemed small and cramped.

hk mr556 review controls trigger safety
At this price point, the trigger and trigger guard needs some work.

On a positive note, you’ll find an ambidextrous safety and a reversible charging handle. To finish off the controls, you’ll find a basic magazine and bolt release.

hk mr556 review charging handle
I’m not sure what the pro(s) would be of a reversible charging handle over a true ambidextrous one, but I’d prefer a true one regardless.

How We Tested

Ammo Used

With the ammo being supplied to us, we shot what we could get our hands on.

There was a variety of FMJs being loaded in various magazines, so I’m not 100% sure exactly what I was shooting. However, I had no problems with any of the ammo that I put through it.

Score Card

Reliability (10/10)  

Simply put, it’s reliable.

Ergonomics (10/10)

AR-15s are pretty ergonomic in nature, so when you add some upgraded furniture, they get even better.

Customization (7/10)

With many proprietary parts, you may have some issues customizing it.

Appearance (7/10)

It looks about as standard as it gets.

Value (8/10)

I still gave it an 8 due to the reliability and accuracy, but the price seems too high.


Aimpoint Duty RDSAimpoint Duty RDSCheck Price
Strike Industries LINK ForegripStrike Industries LINK ForegripCheck Price

Aimpoint Duty RDS

The Aimpoint Duty RDS features a 2 MOA dot that can run for 30,000 hours on brightness setting 7.

It has four night vision compatible settings and is submersible to 80 feet. While it definitely doesn’t fall into the budget category of optics, you get what you pay for.

hk mr556 review with aimpoint drs mounted
The 2 MOA dot is great for medium-range distances.

Strike Industries LINK Foregrip

I’m a huge fan of curved foregrips. The LINK is made out of 6061 T6 aluminum, which makes it very durable.

It’s lightweight, offers a barricade stop functionality, and comes in several colors if you want to get fancy with it.



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Another reliable gas piston AR, the IC-SPR will also save you about $1,000.

It features ambidextrous controls, a fluted barrel, and a free-floating rail. Oh yeah, and it comes with backup sights, which at this price point, every rifle should.

Daniel Defense DDM4 V7

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The most affordable of the ones mentioned, the DDM4 V7 will still not disappoint. It’s reliable, accurate and fully ambidextrous, in addition to having some great upgraded furniture. I’ve personally tested this one out and had a blast.

For more info, check out our DDM4 V7 review.

Final Thoughts

I know I value unbiased and honest opinions, so that’s what I strive to deliver.

While the MR556A1 has been battle-proven to be reliable and accurate, which I agree with, I honestly don’t see the value for a civilian to justify the price. There is nothing “wrong” with the gun, but I think there are plenty of much more affordable rifles that are just as good for the average shooter.

If you have money burning a hole in your pocket though, and are looking for a gas piston-driven AR, it couldn’t hurt to check the MR556A1 out for yourself.  

Written by Ryan Domke
Ryan Domke photo Ryan Domke is a freelance writer, photographer, and social media consultant with a passion for guns and tactical gear. He works with some of the largest manufacturers in the firearms industry, allowing him the opportunity to continuously learn from and knowledge share with the 2A community. Ryan has contributed his writing expertise to numerous reputable publications, including Guns.com, Cheaper Than Dirt, Springfield Armory's 'The Armory Life,' Smith & Wesson's 'The S&W Bench', and The Mag Shack. When he’s not spending time with his family, you’ll likely find him at the range or starting a new DIY project.


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