Heckler&Koch MR556A1 User Manual

MR556A1

OPERATOR’S MANUAL

Covering MR556A1

5.56 x 45 mm Rifle &

MR556A1 Upper Receiver Kit

SAFETY PRECAUTIONS

CAUTION: Read these safety rules before handling the firearm!

Read this operators manual before handling your firearm. The following safety rules are placed in this manual by HK as an important reminder that firearms safety is your responsibility. If handled improperly firearms can be dangerous and can potentially cause damage to property, serious injury, or death.

1. Never point a firearm at anyone, or in any direction other than a SAFE direction, i.e.

downrange.

2. Treat all firearms as if they are always loaded.

3. Keep your finger off the trigger and outside of the trigger guard until your sights are aligned on the target.

4. Keep your finger off the trigger and outside of the trigger guard while loading or unloading the firearm.

5. Keep your finger off the trigger and outside of the trigger guard while slinging the firearm or while carrying it.

6. Be sure of your target and the back stop beyond.

7. Never give a firearm to or take a firearm from anyone unless the action is open and the magazine and/or chamber are free of any ammunition or brass.

8. Be sure that the ammunition you are using is factory loaded, is of the correct caliber for the firearm in which it is to be used, and that it is not damaged in any way.

9. Before firing, remove the magazine from the firearm, lock the bolt open, make sure the chamber is clear of any ammunition or brass, and check the barrel of the unloaded firearm for any possible obstructions.

10. Before firing any firearm that is unfamiliar to you, make sure that you understand

exactly how it functions. A lack of familiarity with the firearm can result in serious

accidents. Attend a certified training course on any firearm which you intend to use or with which you are not sufficiently familiar.

11. Always wear hearing and eye protection when using your firearm.

12. Keep all body parts, particularly the hands and fingers, away from the muzzle to avoid injury or burns.

13. Be sure that parts of the hand do not touch or interfere with the action.

14. Firearms should be stored separately from ammunition and beyond the reach of

children, and/or any untrained individuals.

15. Avoid the use of any alcoholic beverages or drugs before and during the use of any firearm.

16. Discharging firearms in poorly ventilated areas, cleaning firearms, or handling

ammunition may result in exposure to lead, a substance known to be associated with

birth defects, reproductive harm, and other serious injury. Have adequate ventilation

at all times. Wash hands thoroughly after exposure.

17. To make the firearm safe, one must ensure the chambered round is removed during the clearing procedure. Removal of the rifle’s magazine does not remove the chambered round. This can only be done with the rearward movement of the bolt after the magazine is removed.

MR556A1

OPERATOR’S MANUAL

Covering the MR556A1 5.56 x 45 mm Rifle

and MR556A1 Upper Receiver Kit

WARNING: A firearm has the capability of taking your life or the life of someone else! Be extremely careful with your firearm. An accident can occur at anytime and is almost always the result of not following basic safety rules.

STOP! KNOW HOW TO CLEAR THIS FIREARM BEFORE ATTEMPTING TO OPERATE. SEE PAGE 5

Global Website: www.heckler-koch.com • American Website: www.hk-usa.com

Every attempt has been made to ensure the accuracy of this information, however errors or changes

may occur. Speciﬁcations and models subject to change without notice.

Tel: (706) 568-1906 • Fax: (706) 568-9151

Heckler & Koch

5675 Transport Boulevard

Columbus, Georgia 31907

TABLE OF CONTENTS

Safety Precautions ................................................................... Inside Cover

Clearing ......................................................................................................5

Section 1 Introduction ................................................................................................6

Section 2 Nomenclature and Description .................................................................7

Section 3 Function and Op er a tion ..........................................................................12

Section 4 Sights, Sight Adjustment and Aiming ......................................................15

Section 5 Ammunition ..............................................................................................19

Section 6 Instructions for Use ...................................................................................20

Loading the Magazine .............................................................................20

Loading the Riﬂe ......................................................................................20

Firing the Rie ..........................................................................................22

Unloading the Riﬂe ..................................................................................23

Section 7 Disassembly and Assembly ......................................................................24

Disassembly of the MR556A1 ..................................................................24

Assembly of the MR556A1 .......................................................................30

Function Check .......................................................................................37

Magazine Disassembly .............................................................................38

Magazine Assembly .................................................................................40

Section 8 Cleaning and Main te nance .....................................................................42

Lubrication ...............................................................................................43

Section 9 Troubleshooting Prob lems and Re pair ....................................................46

Section 10 Exploded Diagram and Parts List ............................................................48

Section 11 Speciﬁcations ...........................................................................................51

Warranty Registration ...............................................................................51

Section 12 MR556A1 Upper Receiver Kit Supplement ..............................................52

Firearms Service Record ....................................................................................................56

SECTION 1 — INTRODUCTION

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 manufactured 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-oating 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 MR5556A1

and an extended latch charging handle makes operating the rie 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 design innovations of the USA and Germany into one new product.

SECTION 2 — NOMENCLATURE & DESCRIPTION

Fig. 1 – MR556A1 Right and Left Views

1. Compensator – Bird cage style ﬂash hider is screwed to the end of the barrel and helps compensate for muzzle rise during ﬁring.

2. Gas Block – Directs the expended gas from the gas port hole in the barrel and pushes

the piston rearward, pushing the piston rod and bolt carrier rearward (deﬁned in more detail in the cycle of operation). Contains an attachment point for the optional HK folding front sight.

3. Free Floating Rail System (FFRS) – The HK FFRS is a free-oating detachable rail system

with four-quadant MIL-STD-1913 (Picatinny) rails that can mount a variety of accessories including sights, scopes, a forward grip, lights, laser aimers, bipods, and sling hardware. The bore sight alignment of aiming devices is repeatable (no re-zeroing required) when the

Free Floating Rail System is removed and reinstalled on the rearm. The Free Floating Rail

System is removed and reinstalled with a 5 mm Allen wrench.

4. Upper Receiver – The upper receiver is a ﬂat-top design with an integral MIL-STD-1913

(Picatinny) rail that provides support for the barrel, FFRS, gas system, and bolt carrier

assembly. It has a case deﬂector and ejection port. It connects to the barrel and barrel socket. The piston rod is guided through the upper receiver by a bushing and activates the bolt carrier. The charging handle is a part of the upper receiver as is the forward assist and ejection port cover. The upper receiver is made from an aluminum forging.

5. Charging Handle – Allows the operator to chamber or clear a round and cock the ﬁrearm. It also provides for initial charging of the ﬁrearm. The charging handle is locked in the forward position during ﬁring to prevent injury to the operator. An enhanced charging

handle with an extended catch is available on the MR556A1.

6. Selector/Safety Lever – Allows the operator to select the mode of ﬁre and place the ﬁrearm on safe. The selector lever is manually activated and unlike competing AR systems, can be switched to safe even if the hammer is not cocked.

7. Trigger – When activated by the operator, initiates the ﬁring sequence. Located inside the lower receiver, the trigger when squeezed with the ﬁrearm loaded and off “safe” will

re the gun, “SEMI-AUTOMATIC” will re one round each time the trigger is pulled. The

MR556A1 uses a proprietary HK two-stage trigger for optimal accuracy.

8. Trigger Guard – The trigger guard protects the trigger. It can be lowered by depressing the detent with a pointed implement, allowing the use of heavy gloves or mittens to be used to ﬁre the riﬂe.

9. Bolt Catch/Bolt Release – The bolt catch/release is manually operated. When the bolt carrier is pulled fully to the rear, the bottom of the bolt catch/release is pressed by the operator and then the bolt will be captured. To release the bolt, simply press the top of the bolt catch/release. The bolt catch/release is also automatically activated when ﬁring the last round in a magazine.

10. Sliding Buttstock – Attached to the rearm via the receiver extension. The sliding buttstock is ambidextrous and adjustable to 6 positions for length of pull by pressing in

on the rear portion of the Release Lever. It also contains the rear sling attachment points. Many optional buttstocks can be attached to the MR556A1 as long as they ﬁt on the

Receiver Extension (Buffer Tube), which has MIL-SPEC cross sectional dimensions.

11. Forward Assist – Ensures that the bolt is fully closed and locked. The forward assist is

used when a round is not fully chambered. You can push on the forward assist until the bolt seats the cartridge fully into the chamber. It will return to its rearward position by spring pressure. It can also be used to silently load the ﬁrearm.

NOTE: Both the pivot pin and the rear takedown pin are special precision “target rifle” pins. For disassembly and reassembly, a center detent in the shaft of the pin must be engaged under pressure and held to move the pins back and forth. DO NOT FORCE THE PINS. Forcing the pins could damage the rifle and such damage is not covered under the HK warranty. Contact HK Customer Service with any questions, TEL: 706568-1906, EMAIL: cs@heckler-koch-us.com.

17. Magazine – Holds cartridges ready for feeding and provides a guide for positioning cartridges for stripping and chambering. The magazine provides reload capabilities for sustained ﬁring. The HK 30-round steel magazine and optional 20-round steel magazine have a steel follower that will not cant during the feeding process. The spring is stronger and more reliable than standard magazine springs. The MR556A1 can be used with other high quality magazines of all capacities.

18. Magazine Catch/Magazine Release – Holds the magazine (in place) in the magazine well and allows the operator to release the magazine and remove it from the ﬁrearm. The magazine catch is activated automatically when the magazine is properly inserted into the magazine well. The magazine catch is spring loaded and when the button is depressed, the magazine will drop free from the ﬁrearm when this control is activated.

19. Lower Receiver – Contains the ﬁre control system for the ﬁrearm. The lower receiver contains the hammer, trigger, disconnector, sear, magazine well, magazine catch/release, bolt catch/release, selector/safety lever, buttstock assembly with buffer and recoil spring, pistol grip and trigger guard. The lower receiver is made from an aluminum forging and provides a beveled magazine well to ease reloading.

12. Case Deﬂector – Built into the upper receiver, deﬂects the cartridge cases away from the operator.

13. Ejection Port Cover Assembly – The ejection port cover is attached to the upper receiver and is spring loaded. It will open automatically if the charging handle is pulled to the rear or if the ﬁrearm is ﬁred and can be manually closed at any time. It closes over the ejection port to prevent sand, dust, etc. from entering the chamber. It should remain closed when the ﬁrearm is not being ﬁred.

14. Barrel Assembly – The chamber accepts the cartridge for ﬁring and directs the projectiles down range. The barrel is cold hammer forged and has standard land and groove riﬂing with a 178 mm (1 in 7 inch) twist. The barrel is pressed into the upper receiver assembly and held in place by the threaded barrel nut.

15. Locking Screw, Free Floating Rail System (FFRS) – The Free Floating Rail System is fastened with the locking screw to the forward extending barrel locking bushing. Fastening and positioning of the Free Floating Rail System on the bushing is positive and ensures

maintenance of zeroing on any sight system which has previously been attached to the rail after removal and remounting of the rail. The Locking Screw is captive and should not be completely removed, it can be tightened and loosened by using a 5 mm Allen wrench.

16. Pivot Pin – The pivot pin allows the upper receiver to pivot when the rear takedown pin is depressed. When both the pivot pin and rear takedown pin are depressed, the upper and lower receiver groups can be separated. The pivot pin is captive and should not be removed. Both the pivot pin (front takedown) and rear takedown pin have locking shafts that need to be pressed while the pins are depressed and engaged.

20. Pistol Grip – The pistol grip is made so it can be used by a left or right handed shooter.

It has a trapdoor on the bottom so extra batteries, small tools, or other accessories may be stored. Other AR-type pistol grips can also be installed.

21. Rear Takedown Pin – When the rear takedown pin is depressed, it allows the upper receiver to pivot on the front pivot pin. This pin is captive and should not be removed. Like the pivot pin (front takedown pin), the rear takedown pin has a locking shaft that needs to be pressed while the pins are depressed and engaged for disassembly and reassembly.

22. Buttstock Release Lever – The buttstock release lever locks the telescopic buttstock to

the tubular rear buttstock extension. The buttstock is adjustable in length in 6 positions.

23. Rear (Diopter) Sight – proprietary HK sight used on many HK ﬁrearms, attaches to the MIL-STD-1913 top rail of the upper receiver.

24. Front Sight – proprietary HK sight used on many HK rearms, attaches to the MIL-STD1913 top rail of the Free Floating Rail System (FFRS).

25. Front (Flip up) Sight – proprietary HK sight attaches to the gas block, folds down when

not in use.

INTERNAL PARTS NOMENCLATURE

Muzzle – The muzzle is the area at the end of the barrel and the last area that the projectile

touches before it exits the bore.

Bore – The part of the barrel that the projectile travels through from the chamber to the muzzle and contains lands and grooves which make the projectile rotate.

Chamber – The chamber is the area where the cartridge is seated and the initial phase of ﬁring occurs.

Bolt and Carrier Assembly – Provides stripping, chambering, locking, ring, extraction, and

ejection of the cartridges using the recoil spring and projectile propellant gases for power. These parts are made of the highest quality steel.

Bolt – The bolt locking lugs rotate and lock the barrel and bolt together prior to cartridge ignition.

Extractor – The extractor grabs the rim of the cartridge case and pulls the case out of the chamber. The extractor spring and buffer provide constant pressure on the rim until the

case is ejected.

Ejector – The ejector pushes against the cartridge base under constantly spring tension

and once the cartridge or case is extracted and clears the front of the ejection port, the

cartridge or case is ejected from the ﬁrearm.

Cam Pin – The cam pin allows the bolt to cam inside the bolt carrier, which allows the bolt

to lock into the barrel extension when fully forward and cams to unlock when the carrier is

pulled to the rear.

ASSEMBLY GROUPS

Firing Pin – The ring pin will strike the primer and initiate the ring sequence once the

trigger is pulled. The ﬁring pin will only protrude through the face of the bolt when the bolt is fully locked forward.

Firing Pin Safety Spring – Prevents an accidental discharge in the event of dropping or

jolting the gun.

Firing Pin Retaining Pin – Retains the ring pin in the bolt carrier.

Recoil spring and buffer – The recoil spring provides constant pressure on the bolt carrier and holds the bolt in a locked forward position. The buffer has tungsten granules that act

as a anti-bounce back mechanism. One type of buffer serves all barrel lengths.

Buffer detent – Captures the buffer and spring and when depressed, releases them for removal.

Hammer – The hammer, when released by the trigger, strikes the ﬁring pin. The hammer returns when the bolt carrier pushes back under recoil, the hammer makes contact with the disconnector and will release from the disconnector when the trigger is released. The hammer remains cocked under spring pressure.

Trigger – The trigger, when squeezed, releases the hammer and returns under spring tension.

Disconnector – Captures the hammer when it is cocked to the rear and releases the hammer to the sear when the trigger is released. The disconnector then returns to its original position under spring tension.

Fig. 2 – MR556A1 Major Assembly Groups

1. Lower Receiver Assembly - contains the Buttstock assembly (holds buffer and recoil spring), pistol grip, selector lever, trigger group, trigger guard, magazine catch/ release, bolt catch/release, magazine well, pivot pin and take down pin.

2. Buffer and Recoil Spring

3. Charging Handle Assembly

4. Upper Receiver Assembly - contains the forward assist, case deﬂector, ejection port

cover assembly, Free Floating Rail System, gas block (with folding front sight point),

compensator, barrel, gas piston and piston rod.

5. Bolt Carrier Assembly

6. Magazine Assembly

SECTION 3 — FUNCTION AND OPERATION

The function and operation of the MR556A1 is similar to that found in semi-automatic

rearms and consists of eights steps: (1) Feeding, (2) Chambering, (3) Locking, (4) Firing, (5) Unlocking, (6) Extracting, (7) Ejecting, and (8) Cocking.

These eight steps are explained below with a brief description of what occurs inside the

riﬂe during each step. Assume that a full magazine is loaded in the riﬂe with the magazine follower spring forcing the follower and thus the top cartridge into the path of the bolt and the bolt is locked to the rear.

(1) Feeding. The bolt is released from the bolt catch, either by deploying and then

releasing the charging handle or by depressing the bolt catch. The bolt assembly moves

forward, being driven by the expansion of the recoil spring. The bottom locking lugs on

the bolt head act as a feed pawl, striking the top cartridge off the magazine and moving the cartridge towards the chamber in rear of the barrel.

(2) Chambering. The recoil spring continues to drive the bolt assembly forward until the bolt head seats the cartridge into the barrel’s chamber. Chambering is complete when the

extractor snaps into the extracting groove on the cartridge and the ejector is forced into

the face of the bolt.

(3) Locking. Locking occurs when the bolt reaches its limit of forward travel. When the bolt is moving forward, the cam pin orients the bolt head by ensuring that the locking lugs on the bolt head will pass between the gaps of the locking lugs located on the barrel

extension (chamber). The bolt then strikes the back of the barrel and then stops. The

action spring continues to move the bolt head carrier forward, thus causing the cam pin to pivot on the bolt head’s raceway. This action pivots the bolt head and rotates the bolt head’s locking lugs counter-clockwise until they engage the locking lugs on the barrel

extension. The bolt assembly is now locked into the upper receiver.

(7) Ejecting. Ejecting throws the empty cartridge case out of the receiver. As soon as the bolt has drawn the cartridge case clear of the chamber, the force of the ejector spring and plunger pushes the cartridge case head away from the bolt face. This causes the forward end of the cartridge case to move outward to the right. A deﬂector on the outside of the upper receiver deﬂects the cartridge case away from operator.

(8) Cocking. Cocking occurs when the hammer is forced into position for ring the next

cartridge. This happens as the bolt carrier assembly travels toward the rear. The bolt carrier assembly forces the hammer back and rides over it. The hammer is caught by the disconnector if the trigger is still held to the rear and by the trigger’s sear surface if the trigger has been released.

SELECTOR/SAFETY LEVER FUNCTION

NOTE: The MR556A1 has ambidextrous selector/safety levers, that is safety levers located on both sides of the lower receiver. Either lever can be manipulated and moves the lever on the other side. Unlike many AR-style firearms, the selector/safety levers of the MR556A1 can be placed on the “SAFE” position even if the MR556A1 is not cocked.

“SAFE POSITION” – Place the selector lever with the point facing towards the closed white box containing a bullet symbol with an “X” over it (towards the muzzle, Fig. 3).

“SEMI-AUTOMATIC POSITION”– Place the selector lever with the point towards the closed red box containing a red bullet symbol in it (straight up position) (Fig. 4).

(4) Firing. Firing occurs when the ring pin strikes the primer in the head of the cartridge.

When the trigger is pulled, the trigger’s sear surface disengages from the hammer’s intercept notch and the hammer releases. The hammer moves forward under pressure from the hammer spring, disengaging the drop safety, striking the ﬁring pin, and overcoming the inertia of the ﬁring pin spring. This drives the ﬁring pin against the primer, which in turn ignites the propellant in the cartridge case and propels the bullet through the barrel.

(5) Unlocking. Unlocking occurs after a cartridge is ﬁred. As the bullet is forced through

the barrel by expanding gases, a small amount of gas enters through the gas port into the gas block. The gas block features a small expansion chamber that quickly lls up with gas. The gas then hits the front of the gas piston, causing the three piston rings to expand, and

driving the gas piston rearwards. Because the pusher rod is mounted in the gas piston, the pusher rod moves back as well. The back of the pusher rod hits the anvil (string surface) on top of the bolt head carrier, causing the bolt head carrier to move rearwards. As the bolt carrier assembly moves rearward, the bolt cam pin rotates and unlocks the bolt from

the locking lug recesses in the barrel extension. The unlocked bolt is now ready to move

rearward. Any remaining gas follows the bullet out of the muzzle.

(6) Extracting. Extracting removes the empty cartridge case from the chamber. As the bolt unlocks, the bolt rotates slightly counterclockwise, causing the extractor to rotate the cartridge case within the chamber. The expanded case breaks contact with the chamber walls, allowing extraction to occur.

Fig. 3 – SAFE Fig. 4 – SEMI-AUTO

SECTION 4 — SIGHTS, SIGHT ADJUSTMENT, AND AIMING

MR556A1 riﬂes can accommodate a wide variety of optical and mechanical (iron) sights.

HK DIOPTER SIGHTS

For models with HK Diopter rotary sight sets, the sights are installed on the MIL-STD1913 (Picatinny) rail with a Phillips #2 screwdriver or the HK sight tool (Fig. 5 & 6). Do not

over tighten the screws.

Fig. 5 – Front Diopter Sight Fig. 6 – Rear Diopter Sight

For optimal sight use and the longest sight radius, the front sight is installed on the

most forward portion of the MIL-STD-1913 rail and the rear sight is installed on the most rearward portion of the MIL-STD-1913 rail (located on the upper receiver). Sight adjustment is as follows:

The sight adjustment is a rear sight adjustment, so the movement of the sight will be in the same direction the shooter wants the impact of the round to move. If the hit is to the right of the intended location, then the sights and the impact must be moved left. Any corrections which may be required when sighting-in the weapon may only be performed by adjusting the rear sight for elevation or windage. MR riﬂes are designed to

be sighted in at a range of 100 meters. REMEMBER THIS FORMULA: LL=C (Lower or Left = Clockwise rotation)

ELEVATION ADJUSTMENT (Alternative method without sight tool)

Use of the HK Sight Adjustment Tool (HK ID # 300009) is always recommended to adjust the windage and elevation on any HK ﬁrearms equipped with standard diopter sights. However, some needle nose pliers can be substituted in the event that a sight adjustment tool is not available to perform range adjustments.

Ensure that the MR556A1 is unloaded before performing any adjustment to the sights. Use needle noose pliers with smooth jaws rather the serrated jaws as the serrated surfaces may cause chips and burrs on the spring loaded catch bolts. Simply insert the jaws onto the small shelf on the catch bolts and carefully squeeze while simultaneously rotating the drum. This action withdraws the catch bolts and allows the drum to be rotated either clockwise or counter-clockwise. To lower the point of impact, rotate the drum clockwise and to raise the point of impact, rotate the drum counter-clockwise. Ensure that the catch bolts engage the vertical slots located on the inside of the drum after removing the needle nose pliers.

WINDAGE ADJUSTMENT

Point of impact, left: Loosen clamping screw on top of sight base (Fig. 8). Turn adjusting

screw on the right side counterclockwise (Fig. 9) in accordance with the required

correction. Then retighten clamping screw. This will move the impact to the Right.

Point of impact, right: Loosen clamping screw (Fig. 8). Turn adjusting screw clockwise (Fig. 9) until the required correction has been performed. Then retighten clamping screw.

This will move the impact to the Left.

NOTE: Each revolution of the Windage screw will move the impact of the round 15.2 cm (6 inches) at 100 meters.

TROY ACCESSORY SIGHTS

Some MR556A1 ries are supplied with Troy Industries Micro Folding Sights. Aiming and

sight picture are similar to using the HK diopter sights.

ELEVATION ADJUSTMENT

Insert elevation adjustment tool into the rear sight cylinder so that the wedges of the tool engage in the two slots in the cylinder which contain the catch bolts. Press Phillips-head screwdriver downward into the adjustment tool and hold ﬁrmly. Rotate rear sight cylinder

manually in the desired direction (Fig. 7).

After correction withdraw Phillips-head screwdriver and remove elevation adjustment tool. The catch bolts will then re-engage in the slots. After performing the elevation adjustment set the desired aperture again.

NOTE: One-quarter turn of the rear sight drum will move the impact of the round approximately 3.8 centimeters (1.5 inches) at 100 meters

Fig. 7 – Rear Fig. 8 – Clamping Screw Fig. 9 – Windage Sight Adjustment (to tighten turn clockwise) Adjustment

Fig. 10 – Installing front TROY sight Fig. 11 – Tightening front TROY sight

INSTALLING TROY ACCESSORY SIGHTS (FRONT)

1. Unscrew clamping assembly and place the sights at the desired location on the

Picatinny rail (Fig. 10).

2. Apply one drop of tread locking compound to the exposed threads of the clamping

screw. Replace the clamping plate and tighten the clamping screw while pushing

sight forward against the cross-slot (Fig. 11). To raise the sight, grasp and pull up

until the sights locks in the upright position. To fold the sight, depress the button on

the left side of the base and fold down. (Fig. 12)

Fig. 12 – Folding (lowering) Fig. 13 – Lowered sight TROY front sight TROY front sights

INSTALLING TROY REAR SIGHTS

1. The rear TROY sight installs similar to the front sights. Unscrew clamping assembly

and place the sights at the desired location on the Picatinny rail.

2. To raise the sight, grasp and pull up until the sights locks in the upright position. To fold (lower) the sight, depress the button on the left side of the base and fold down.

(Fig. 14-16)

Fig. 14 – Rear Sight Fig. 15 – Lowering Fig. 16 – Rear sight Rear Sight folded (lowered)

FRONT SIGHT ADJUSTMENT ZEROING

1. Fire a group of four (4) shots and measure the average distance for point-of -aim to

point-of-impact.

2. Adjust front sight for elevation only.

3.Windage adjustments are made with the rear sight.

4. Conﬁrm zero with a group of four aimed shots and adjust is necessary

Fig. 19 – Rear Sight Fig. 20 – Windage adjustment

REAR SIGHT ADJUSTMENT

Windage adjustment can be made by inserting a pointed object (like a bullet tip) or a ﬂat object (like a screwdriver or coin) into the coin slot and turning the adjustment wheel. To move the bullet impact right, turn the adjustment wheel to the right/clockwise. To move

the bullet impact left, turn the adjustment wheel to the left /counter clockwise (Fig. 19 &

20).

Fig. 21 – Rear Sight Fig. 22 – Changing aperture

The Troy rear sight also offers a choice of two ﬂip-style apertures, both large and small

(Fig. 22). The large aperture is for close engagement and the small aperture is for more

distant shooting. Generally the large aperture works best for alignment with the front sight and for short and medium ranges. Elevation does not change when switching apertures.

For long range shots, the small aperture can be ipped into position by nger pressure on

the top of the rear sight.

Value for 1 click of adjustment Troy Micro Sights 100 meters 200 meters 300 meters

M4/HK416/MR556A1 sight radius .50 MOA 5/8” 1-1/8” 1-5/8”

Fig. 17 – Front sight adjustment Fig. 18 – Using a bullet tip

to adjust the front sight FRONT SIGHT ADJUSTMENT

To move the bullet impact up, turn the adjustment wheel to the right/clockwise (Fig. 17

& 18). To move the bullet impact down, turn the adjustment wheel to the left/counter

clockwise (Fig. 18 & 19).

INSTALLING THE OPTIONAL HK FLIP-UP FRONT SIGHT

Press front sight onto front sight holder until the axes holes of front sight and front sight holder are aligned. Push through front sight axles all the way, from the right to the left and secure the front sight axles by snapping the retaining clip. Check function of foldable front sight (Fig. 23 & 24).

Fig. 23 Fig. 24

Fig. 25

A wide variety of mechanical, optical, and telescopic sights can be installed directly on

the upper MIL-STD-1913 rail (examples, Fig. 25), either on the upper receiver portion of the rail or on the Free Floating Rail System. For sight alignment and zeroing, follow the

instructions of the sight and scope manufacturers. General mechanical sight alignment

information is depeicted in Fig. 26-27.

NOTE: Do not overtighten scopes, aimers, or any other accessories mounted on any of the MIL-STD-1913 (Picatinny) rail surfaces of the MR556A1. Overtightening can damage the rails.

Fig. 26 – Correct Aiming, HK diopter sights (left) and TROY sights (right)

SECTION 5 — AMMUNITION

By using ammunition with match bullets or other match grade ammunition the MR556A1 will achieve the best level of accuracy. Use ammunition of the appropriate caliber and of

recent manufacture. The MR556A1 is chambered for 5.56 x 45 mm ammunition and will

functioned safely and reliably with most high quality 5.56 mm and Caliber .223 Remington ammunition.

NOTE: Use only high quality 5.56 x 45 mm NATO or caliber .223 Remington ammunition in the MR556A1 rifle. Damage caused by the use of improperly assembled or remanufactured ammunition may void the HK Warranty. Do not use ammunition assembled with corrosive components (primers, propellants, etc.).

The MR556A1 is designed to use ammunition made to NATO or SAAMI specications.

DO NOT USE

• Reloads or remanufactured ammunition. Beware of military surplus, foreign or outdated

ammunition.

• Non-jacketed or exposed lead ammunition.

• Corrosive ammunition (primer and/or propellant).

• Empty cases as “dummy“ (inert) rounds, as damage may result. Use complete dummy

rounds available for training purposes.

• Any ammunition that exceeds NATO or SAAMI (Sporting Arms and Ammunition

Manufacturers’ Institute) pressure limits.

• Cartridges that are not 5.56 x 45 mm or Caliber .223.

• Seriously corroded ammunition.

• Dented Cartridges.

• Cartridges with loose bullets.

• Cartridges exposed to extreme heat above 135°F (57°C) until they have cooled.

• Use only authorized ammunition that is manufactured to NATO and SAAMI specs.

• Ammunition that is wet or dirty.

Fig. 27 – Aiming Errors

WARNING: Only use ammunition designed to NATO and SAAMI specifications that is factory-loaded, undamaged, and of the correct caliber. The use of low powered cartridges could lead to functional stoppages (including bullets stuck in the barrel) and is not recommended.

+ 21 hidden pages

Heckler&Koch MR556A1 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual