A direct descendent of the HK416, the MR556A1 is a
semi-automatic rifle developed by Heckler & Koch as a premium level
commercial/civilian firearm with match rifle capability. Like the
HK416, the MR556A1 is a major product improvement over conventional
AR-type carbines and rifles.
The MR556A1 uses the HK proprietary gas piston
operating system, employing a piston and a solid operating “pusher” rod
in place of the gas tube normally found in AR15/M16/M4-style firearms.
This method of operation virtually eliminates
malfunctions that are common to direct impingement gas systems since hot
carbon fouling and waste gases do not enter the receiver area. This is
the same key feature critical to the success of the HK416 rifles used by
leading military and law enforcement customers.
The MR556A1 is produced in the USA using American
and German made components. The MR556A1 uses many of the same
assemblies and accessories originally developed for the HK416 including
the HK free-floating four-quadrant rail system.
The HK Free Floating Rail System (FFRS) handguard
has four MIL-STD-1913 “Picatinny” rails and allows all current
accessories, sights, lights, and aimers used on M4/M16-type arms to be
fitted to the MR Series. The HK rail system can be installed and removed
with simple tools and returns to zero when reinstalled.
The MR556A1 also has a Picantinny rail machined
into the top of its upper receiver for mounting optics and mechanical
sights. Unlike earlier prototypes, major subassemblies, including the
MR556A1 upper receiver/barrel assembly, are fully interchangeable with
other high quality AR-style firearms. MR556A1 upper receiver kits can be
used to retrofit competing legacy AR systems.
Like the famous HK416, the MR556A1 uses a
German-made barrel produced by Heckler & Koch’s famous cold hammer
forging process. The highest quality steel is used in this unique
manufacturing process producing a barrel that provides superior accuracy
and long service life.
But unlike the HK416, the MR556A1 does not use a
chrome-lined barrel. Chrome-lining can sometimes mask bore
imperfections and negatively affect accuracy. For the new series of
Heckler & Koch semi-automatic MR rifles, HK designers and engineers
believe best accuracy comes with an unlined bore.
Used with the HK Free Floating Rail System, the
barrel does not touch the handguard, ensuring the barrel is truly
free-floating for maximum accuracy.
The unchromed barrel has an internal profile of 6
lands and grooves with a 1 in 7 inch (178 mm) twist. It is also
moderately “swagged” with a slightly smaller internal diameter at the
muzzle end than the chamber end. This feature has a positive effect on
bullet accuracy and velocity. The thick, heavy contour 16.5-inch
MR556A1 barrel also contributes to its excellent accuracy.
A precise enhanced two-stage trigger adds
significantly to the accuracy of the MR556A1 and an extended latch
charging handle makes operating the rifle with a telescopic sight
easier. The retractable buttstock can be locked into a solid, non-moving
position by tightening an Allen screw in the bottom of the stock.
Special target rifle takedown pins ensure the upper and lower receivers
are firmly mated for accurate performance.
Designed to function with a wide variety of high
quality 5.56 x 45 mm ammunition, the MR556A1 uses a C.I.P. dimensioned
chamber (a chamber with dimensions specified by the Commission
Internationale Permanente).The MR556A1 also functions reliably with most
quality Caliber .223 Remington ammunition.
The MR556A1 is being produced with the same
commitment to quality as German-made HK firearms. By using joint
U.S./German manufacturing, Heckler & Koch leverages the relative
strengths of two continents to make the preeminent AR-type firearm,
combining the designs innovations of the USA and Germany into one new