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H&K MR556A1
by Christopher R. Bartocci

In the 2001 time period the current U.S. military weapon system M16/M4 came under scrutiny during the initial Global War on Terrorism. U.S. Special Operations operators experienced issues with failure to extract, bolts breaking, barrel overheating/ruptures as well as malfunctions in the desert environment. The program commenced in June of 2000. The program was initiated by Jim Schatz and Ernst Mauch of Heckler & Koch, which would become known as the HKM4. Ernst Mauch decided he wanted to pursue similar improvements to the existing M16/M4 weapon systems. Former Tier 1 U.S. Special Operations operator Larry Vickers went to work with Heckler & Koch to develop an improved M4 which would correct the deficiencies they encountered. While visiting H&K on another matter Vickers noticed a blueprint hanging on the wall of former H&K CEO Ernst Mauch of an M4 adapted to a G36 gas system. Vickers knew there was a requirement in his unit for a short barreled (10.4 inch) CQB rifle to replace the Mk18 currently in use. SOCOM had found the short 10.3 inch weapons experienced significantly more malfunctions than the M4 with the 14.5 inch barrel in various operational conditions. Additionally H&K staffers Tom Kivlehan and Bruce Davidson worked along with Mauch, Schatz and Vickers to get this program off the ground and eventual military testing and acceptance.

In August of 2000: USSOCOM held a “PMOD” Conference with industry in Indianapolis to discuss their planned “Platform MODifications” effort they hoped to run to address the many documented deficiencies in the M4. HK staff Mauch, Schatz, and Volker Kurtz were present and briefed the first drawings of a monolithic (one piece upper receiver and rail system) M4-style upper with a G36-style op rod gas system. The proposal was reportedly well received by many military program staff (including Gus Taylor from Crane and the Army’s Steve Holland). As recalled by several people, Colt Defense killed off the PMod program making exclusivity claims to the M4 and that only they could make such modifications to “their M4.” Given the time frame and the lack of cooperation, this spawned the invocation of the SCAR program which would allow SOCOM to pick a new weapon platform. They in fact would be the project manager and could modify “at will” rather than use Colt M4A1 carbines that they could not make changes to due to them being a “TDP” commodity that they would have to go through the big army to change.

Direct gas rifles traditionally show more reliability problems in shorter barrel lengths in extreme conditions. The H&K rifle would keep the ergonomics of the M4 but have the reliability and gas system of the more reliable G36. H&K asked SOCOM to loan them some M4 carbines so they may conduct research and development on their new design. After lengthy legal research it was found that there was no conflict of interest with the government or Colt since no technical data was exchanged and the rifles were provided to H&K. H&K’s approach to this program was similar to that of the British SA80 rifle. They would look at the overall system and then improve upon it. H&K provided the research and development of this new weapon at their own expense and the U.S. government had no responsibility and could walk away from the project at any time. It was agreed by H&K engineers as well as many in the industry that the direct gas system is not the best for the high demands of special operations operators. The environment, heat, inability to properly clean and lubricate the weapon under combat conditions all made the system that much more to take care of. The short stroke tappet, basically another Stoner design in the AR-18 would be cleaner, cooler and more reliable than the legacy system. The rifle created was the HKM4.

The HKM4 looked very similar to the M4 but with some notable changes. Unlike the legacy M4 direct gas operating mechanism, the HKM4 utilized a short stroke tappet system. This major change leads to several enhancements over the legacy system including cooler, less fouling and increased reliability. Heat has always been one of the most serious of problems with direct gas systems. It causes lubrication to dry out which in turn causes malfunctions. Also, the service life of certain parts in the bolt is affected including extractor and ejector springs. The HKM4 using the short stroke tappet system did not have any of these issues: in fact you could fire 5 magazines of 30 rounds and hold the bolt carrier group in your hand without any issue. The bolt was redesigned giving a more durable material, improved extractor and advanced plating of the bolt. The early prototypes utilized an extended carrier key that was part of the bolt carrier. Later it was changed to a machined impact area that was more durable. Due to the piston operating rod, no fouling was introduced to the bolt carrier group at all. Firing several hundred rounds and inspection of the bolt and carrier show little fouling, just some brass chips from the extractor and ejector and what lubricant was applied before firing. The original HKM4 did not have an ejection port dust cover. HK engineers kept the HKM4 in line with the gun its operating system was taken from, the G36, and the G36 did not have one. However, this proved to be problematic, not from a mechanical point of view but perceptional. Customers would view it as cheapening the system and felt it was necessary so H&K provided it on later models. The buffer was much heavier being filled with tungsten powder and the spring was significantly stronger than the legacy. Initially the lower receiver was a standard M4 but H&K redesigned some of the features on the lower including a beveled magazine well. Several attempts were made at developing a rail for the HKM4 including an attempt to install a Knight’s Armament System. Finally a 1-piece rail was designed by H&K that locked in place by a nut that used a locking lug on the bolt to tighten. This rail allowed the barrel to float without interference from the rail. The HKM4 was initially designed with a 10.4 inch barrel but later a 14.5 inch barrel was used.

The magazine the HKM4 was built around was the SA80 magazine that HK designed for the British government when they were brought in to fix this very deficient rifle. The profile of the SA80 magazine well differs from the M4/M16. The British have a magazine for the SA80 which uses solely blank ammunition. There is a tab in the front of the magazine which disallows insertion of live ammunition. The tab notch is visible on the bottom-front of the magazine well and the front portion of the magazine sits much deeper into the magazine well. This is the reason the standard Magpul PMag will not work in the HK416: the constant curve design of the magazine prevents the magazine from seating and locking into the magazine catch. The EMag has the proper profile for use in the HK416 and the SA80 rifles.

Preliminary acceptance testing by SOF came in November of 2004. More than 12,000 rounds were fired at H&K by SOF personnel. The rifle passed all testing and the first 500 were ordered by SOF. Around this time the name was changed from the HKM4 to the HK416 (M4 and M16). Due to a trademark lawsuit filed by Colt Defense, H&K settled out of court. The terms are confidential but part of it was to not use the M4 name. However, the Colt claim to the trademark M4 would soon be challenged by Bushmaster ending Colts trademark of the term M4. The judge found the term M4 in common usage and rendered the trademark void. After fielding, some areas for improvement were found - the most notable being the addition of a firing pin safety. As previously stated, the HKM4/HK416 uses a significantly stronger action spring and heavier buffer than the legacy rifle. The early design used a similar weight firing pin than that of the legacy rifle. Due to the heavier spring and buffer the inertia from the firing pin would cause slamfire conditions with some ammunition. To correct this condition the firing pin safety of the UMP/MP7 was added to the bolt carrier. The firing pin is held in place by a lever that only is disengaged when the top of the hammer lifts the rear of the lever allowing the firing pin to move to strike the firing pin. The barrel profile was lightened due to the rifle being so front heavy when accessories were added.

When the SCAR program came to fruition, Heckler & Koch decided against entering the HK416. At the time, H&K was working and using vast amounts of their resources on the XM8 program. With this, the potential of having a weapon program for the greater green machine was a better investment than the HK416 was to a small number of SOCOM units. Many in the industry felt this was a mistake and felt the HK416 was the ideal SCAR rifle. As it turned out, the U.S. government would later cancel the XM8 program leaving H&K to absorb the costs. As fate would have it, H&K then stirred up a hornet’s nest within both the U.S. military as well as congress. As more and more complaints came out of the war zones about M4s malfunctioning in combat, H&K used both the media as well as congress to expose the issues as well as promote their solution for the problem. The Army was forced by Congressman Tom Coburn to examine the allegations that American troops may not have the best rifle available. The chain reaction caused the Army to conduct Dust Test Two which compared the Colt M4, HK416, HK XM8 and the FN SCAR-Light (Mk 16 Mod 0). The test showed the current issue M4 to be the least reliable, by far. The test consisted of 10 each of the rifles and firing 60,000 rounds per model. The end result was the XM8 127 stoppages, the FN SCAR Light 226 stoppages, the HK416 233 stoppages and the current issue Colt M4 carbine 882 stoppages. Clearly there is a large gap in stoppages seen between the newer carbines and the standard. The results of this test were questioned by both Colt Defense as well as some in the Army but the results stand. This got congress and the army to initiate two different actions. First, for the short term, was a M4 Product Improvement program consisting of three phases. Phase one is procuring 25,000 new M4A1 carbines with heavy barrels, full auto capability and ambidextrous controls. Phase II is an open competition for a new and improved bolt carrier group and forward rail. Phase III is an operating system review to see if there is a better more reliable gas system for this weapons platform. This is the big question. Most of the issues surrounding this debate center on the operating system. Is direct gas impingement as reliable as, or less reliable than, the standard short and long stroke piston designs. The open competition was scheduled for the summer of 2011 and many industry leaders submitted their version of what they felt would be the next U.S. service rifle.

In 2006, the Marine Corps put out a requirement for an Infantry Automatic Rifle. This is to be a lightweight magazine fed rifle that was to replace the heavy belt fed M249. The IAR was to improve the maneuverability and displacement speed over the heavier M240 and M249 belt fed machine guns. Several manufacturers put weapons into the competition but in 2006 developmental contracts were awarded to Heckler and Koch, FN and Colt Defense. The H&K rifle beat out the competition in December of 2009. The H&K M27 is based on the HK416 but has a 16.5 inch heavy barrel as well as a bayonet lug. These Marines have already taken shipments of the new M27.

The MR556A1

Throughout the history of the HK416, the rifle was publicized and touted as being the best combat rifle in the world; but the only problem is if you were not a SOCOM operator or police officer you could not have one. There was no commercial equivalent for the HK416. The HK416 was held in front of an army of firearms enthusiasts like a piece of raw meat that this hungry pack of wolves could not get to. HK had received the request but there were complications in fulfilling it. First the importation laws needed to be met. The uppers could not be imported for commercial sales from Germany due to the fact they could be put on machine guns. So they had to be manufactured here in the United States. Heckler & Koch USA staff fought diligently to prevent another heavily modified semi-auto version like the SL8 was to the G36. The SL8 looked very little like the G36. Thanks to their perseverance the decision to move the takedown pin back on the rifle to prevent its use with standard AR-type lowers was thwarted hence the “A1” suffix in the model name. Certainly many components could be shipped in from Germany but the barrel and lower receiver had to be made in the states. On January 18, 2011 H&K announced the release of the MR556A1 at the 2011 SHOT Show in Las Vegas. With a suggested retail of $3,295, this rifle was meant for the serious shooter/collector.

The MR556A1 has all of the advanced features of the HK416 in a commercial package. First on the scene is the MR223 which was manufactured by H&K in Germany for their commercial market. There was no flash suppressor and it was chambered for the .223 Remington cartridge instead of 5.56x45mm. Due to importation restrictions, H&K set up production in Columbus, Georgia where they import the barrel blank, bolt group, handguard and fire control group from Germany. The lower receiver is manufactured in the U.S. as well as the barrel is finished in the state, making the MR556A1 legal under the importation laws.

The lower receiver is manufactured out of a solid forging and has the beveled magazine well of the HK416. The pistol grip is manufactured by H&K for the most ergonomic fit. There is a storage compartment in the base of the pistol grip as well. The selector lever is ambidextrous. The trigger is what is most unique on this model. Not that it has an excellent 2-stage pull which enhances accuracy but this trigger group can have the safety engaged whether or not it is cocked. This was a mandate for the MR223 to be sold in Germany and carried over to the MR556A1. This is a major enhancement that makes training easier when the safety can always be engaged when clearing the weapon. The bolt catch and the magazine catch are identical to that of any M16/M4 weapon making training simple, or should I say transition training. The HK416/MR556A1 uses a proprietary buffer and spring. Both are significantly heavier than the standard M4. The buffer is filled with a tungsten powder. Both are easily differentiated from others by the big red dot on the face of the buffer and the red paint on the action spring. These parts should never be changed for it will throw off the timing of the action causing damage to the rifle or malfunctions. The buffer retainer pin has been redesigned and strengthened with a 1/4 moon cut which also makes stock installation easier. The receiver extension has 6 positions and the back of the receiver extension has three drain holes for water to exit when handled and fired in watery conditions. The stock is proprietary to H&K as well. The latch is protected inside the stock to eliminate the chance of it unintentionally moving. The rubber buttplate is turned 90° and removed. There are battery storage compartments in the cheek weld area of the stock. Also unique to the MR556A1 is an allen-type tool which is used to disengage the rear takedown and front pivot pin. This also is unique to the MR556A1. To separate the receiver, the tool is pushed into the center of the retainer pin and pushed to detent. When reinstalling the spring is again depressed by the tool and the pins are pushed back in until locked.

The upper receiver is similar to that of an M4. It contains a forward bolt assist as well as a fired cartridge case deflector. The top rail is a Mil-Std 1913 rail. The charging handle has a reversible charging handle latch for left-handed shooters. The barrel extension has a tab extending from the left side that slides into a notch on the bolt carrier. This is an anti-conversion precaution. If one was to try to put a selective fire bolt carrier in the upper receiver it would not close.

The MR556A1 16.5 inch barrel is manufactured with the German exclusive barrel material produced by H&K’s proprietary cold hammer forging process. The barrel is finished in the United States and unlike the HK416, the MR556A1 in not chrome plated. This rifle is designed as a target rifle and H&K felt the barrel would be more accurate without the chrome plating. The barrel has the NATO standard 1 turn in 7 inch twist making the barrel compatible with 55 to 80 grain projectiles. The barrel is topped off with an M16A1-style birdcage flash suppressor. The rifle comes standard with the H&K diopter rear sight and standard front sight as seen on their G3/MP5 weapon systems. Both are removable. The front site can be replaced with a proprietary H&K folding front sight. The sight attaches to the gas block.

The MR556A1 uses the same H&K proprietary gas piston operating systems. The gas is bled from the front of the gas block preventing gases from hitting other people on the sides of the shooter or the shooter himself. The piston has gas rings on the end and is chrome plated. The operating rod assembly fits behind the piston and is a captive unit composed of a piston rod, spring and a guide. This is a short stroke tappet system by which when the round is fired, gas is tapped from the barrel, expands between the piston and the gas block driving the piston to the rear actuating the operating rod. The operating rod strikes the bolt carrier driving it rearward. As the bolt moves rearward the piston rod returns back forward into the gas block ready for the next shot. Unlike the direct gas system, there is no heat or hot gasses deposited into the bolt carrier group to cause fouling.

The bolt carrier is very unique compared to any other carrier in the industry. The MR556A1 has all the most current updates of the HK416. The bolt is high quality German engineering as expected from HK and is plated with a proprietary finish. The firing pin utilizes a spring and the newest feature, which was a requirement from the Norway trials of the HK416, is a captive firing pin retainer pin. This is an excellent enhancement since the firing pin retainer pin is the most lost and damage component in the rifle system. What really makes this bolt carrier unique is a proprietary firing pin safety. An arm locks the firing pin in place preventing it from coming through the bolt to hit a primer unless the trigger is pulled. This is done by the top of the hammer tipping upward disengaging the firing pin safety so the firing pin may strike the primer. Due to the extremely heavy H&K buffer and action spring the HK416 would experience slam fires or the inertia of the firing pin striking the primer and firing the cartridge when the bolt closes and locks. This system prevents this condition.

The MR556A1 weighs in at 9.04 pounds with the iron sights and empty magazine. With the stock fully extended the rifle is 37.68 inches and with the stock fully closed 33.90 inches. The steel H&K 30-round magazine weighs .53 pounds empty. The sight radius is approximately 14.6 inches. The rifle comes with an operator’s manual as well as a plastic carrying case.

The MR556A1 was tested with several magazines. Due to the magazine well not being NATO standard some magazines that work in a standard M16/M4 will not work in the HK416/MR556A1. The magazines tested which fit and worked flawlessly are the H&K High Reliability Magazine, Magpul EMag, OK Industry GI magazines, Lancer L5-AWM (Advanced Warfighter Magazine), Lancer L5 20-round magazines and C-Products 20- and 30-round steel magazines. More than 700 rounds of Silver State Armory 5.56mm M193 ball ammunition was fired with no malfunctions encountered. The recoil was very minimal and due to the heavy barrel the rifle remained on target with easy to control rapid fire. The trigger greatly assisted with accuracy. The rifle shot a consistent 1 MOA group with Silver State Armory 5.56x45mm 77gr Open Tip Match ammunition.

The Heckler & Koch 416 has made a significant impact on the current momentum to replace the M4. As of this writing, not in sales but the introduction and the brilliant marketing and lobbying campaign H&K assembled has brought about the current new individual carbine competition as well as M4 incremental product improvements. Will the HK416 be the next U.S. service rifle? That is the million dollar question but it got us to the competition and to seriously consider if the U.S. soldier is truly armed with the best small arm this nation can provide. However, finally there is now a better rifle and you can have it, the MR556A1. Coming later will be the MR762A1, the commercial version of the 7.62x51mm HK417. H&K has heard the commercial customer and responded.


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