HK416 And The MR556A1

Product Review: The HK416 and the MR556A1

Heckler and Koch (HK) is a German firm known for supplying military and police forces with some of the best firearms currently available. HK rifles have traditionally worked with a system of bolt rollers that lock the action shut, but the company has become more mainstream with its G36 assault rifle, which uses a gas piston system. HK has also applied its considerable experience to troubleshoot and improve the British SA-80 bullpup rifle.

So, what happens when HK takes its considerable design expertise and applies it to America’s standard battle carbine, the M4?

The HK416

The HK416, HK’s product-improved M4, replaces the conventional AR’s gas tube with a solid push rod, helping keep carbon and firing residue out of the upper receiver. The HK416 was originally produced at the request of US special operations troops who wanted a reliable, low-maintenance rifle that would function in all environmental conditions and with or without a sound suppressor.

While the HK416 got its start as a Special Forces rifle, current issuance and usage in the U.S. Special Operations community appears to be limited. Rumors abound about premature parts wear, breakage, and the rifle being too expensive with too many unique spare parts, making field repair difficult.

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However, the HK416 has found success as the USMC’s new Infantry Automatic Rifle and is being used by various military and police departments across the globe, with Norway being a notable user.

The MR556A1 (Civilian Version)

The civilian version of the HK416 is dubbed the MR556A1. It is chambered for 223 Remington and 5.56 NATO cartridges but lacks the chrome-plated chamber and bore of its military counterpart. HK believes that best accuracy comes with an unlined bore, as chrome-lining can sometimes mask imperfections and negatively affect accuracy.

The MR556A1 features a 16.5″ barrel with a 1×7 twist, free-floated and covered by a removable quad rail housing the gas piston and push rod. The rifle uses a crisp, clean two-stage trigger, albeit a bit heavy at around seven pounds.

Improvements over standard AR-15

The MR556A1 has the potential to be far more reliable than a standard AR-15. HK engineers redesigned the bolt, eliminating gas rings and creating a longer, more substantial bolt. The gas piston parts are heavy and beefy, requiring an increased height of the top rail to house them.

Other improvements include a captured firing pin retainer, a firing pin block that locks the firing pin until the trigger is pulled, and a safety lever that can be rotated to safe with the hammer in the forward position.

Range Performance and Compatibility

On the range, the MR556A1 performed flawlessly with various magazines and ammunition. The unique shape of the magazine well may cause fitment issues with some plastic magazines, but USGI aluminum, HK steel, and Surefire’s 60-round quad stack magazines worked fine.

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The unlined barrel lived up to HK’s accuracy claims, shooting as well as expected from a rifle of this quality. The MR556A1 upper receiver proved compatible with other AR-15 lower receivers, although internal parts may differ from other piston ARs.


The MR556A1 has two main drawbacks: weight and price. The rifle’s quad rail handguard and heavy profile barrel result in an empty weight of over eight pounds, putting it in the same class as some AR-10 308 rifles. Additionally, the MR556A1 is substantially more expensive than piston-driven ARs from competing manufacturers.


Despite its weight and price, the MR556A1 boasts an impressive design pedigree and delivers flawless performance. Its improvements over the standard AR-15, such as the redesigned bolt and carrier, firing pin block, and safety lever modification, contribute to increased reliability and functionality.

While it may not be the most cost-effective option, the MR556A1 is a well-engineered and reliable piston-driven AR-15 that showcases HK’s expertise in firearms design and development.


What is the difference between the HK416 and the MR556A1?

The HK416 is the military version, while the MR556A1 is the civilian version. The main difference is that the MR556A1 lacks the chrome-plated chamber and bore found in the HK416.

Why did HK choose not to chrome-line the barrel of the MR556A1?

HK believes that best accuracy comes with an unlined bore, as chrome-lining can sometimes mask imperfections and negatively affect accuracy.

How does the weight of the MR556A1 compare to other AR-15 rifles?

The MR556A1 is relatively heavy, with an empty weight of over eight pounds due to its quad rail handguard and heavy profile barrel. This puts it in the same weight class as some AR-10 308 rifles.

Is the MR556A1 worth the higher price compared to other piston-driven AR-15 rifles?

While the MR556A1 is substantially more expensive than piston-driven ARs from competing manufacturers, it boasts an impressive design pedigree, flawless performance, and several improvements over the standard AR-15. Ultimately, the value of these features will depend on the individual shooter’s needs and preferences.

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