Heckler&Koch MR556A1 User Manual

Page 28

Fig. 6 – Installing Front Takedown Pin

2) Ensure the pivot pin (front takedown pin) and rear takedown pin are “drifted out” to the

right hand side of the receiver.

3) Mount the lower receiver to the upper receiver. Using finger pressure, press the front

pivot pin from right to left so it captures and secures the upper receiver (Fig. 6).

4) Fully close the upper receiver onto the lower receiver. Press the rear takedown pin from

right to left until the rear takedown pin secures the rear portion of the upper receiver to the

lower receiver (Fig. 7).

CAUTION: Any excessive forcing of the takedown pins could damage the URK and

such damage is not covered under the HK warranty. For further information, please

contact HK Customer Service at TEL: 706-568-1906, EMAIL: [email protected].

5) For removal of the MR556A1 Upper Receiver Kit, reverse the assembly procedure.

Fig. 7 – Completing the installation of the MR556A1 Upper Receiver

on the Lower Receiver

NOTE: For Buffer Assembly lubrication, apply a heavy coat of CLP (cleaner, lubricate,

preservative) lube on the HK action spring and HK buffer. Apply a medium coat of CLP

lube to the inside of the buffer tube.

WARNING: Always ensure the firearm is unloaded prior to attempting to perform a

function check. Legacy AR15/M16 platforms require that the hammer be cocked prior

to attempting to place the firearm on “SAFE”.

FUNCTION CHECK

1. Perform clearing procedure (consult operator’s manual for non-HK carbine used or see

the MR556A1 Operator’s Manual) and ensure selector lever is set on “Safe”.

2. Place the muzzle in a safe direction and rack the bolt to the rear three or four times in

quick succession by using the charging handle. The bolt should not bind when traveling

back and forth in the receiver.

3. “SAFE”: Let the bolt go forward and completely go into battery. With an unloaded

carbine and the muzzle in a safe direction, ensure the selector lever is set on “Safe” and

attempt to pull the trigger. The hammer must not fall.

4. “SEMI-AUTOMATIC”: Rotate the selector lever to “Semi-Automatic” (Single Shot) and

with an unloaded carbine and the muzzle in a safe direction, attempt to pull the trigger

and hold to the rear. The hammer must fall.

5. While maintaining pressure on the trigger, rack the bolt and release. The hammer

should be held by the disconnector.

6. Release the trigger. The hammer should be caught by the sear as signified by a metallic

click. Release the trigger completely and re-engage the trigger. Hammer must fall.

7. Insert an empty magazine into the magazine well and pull back on the charging handle.

The magazine follower should engage the bolt catch and lock the bolt to the rear on

an empty chamber.

8. Remove the magazine and allow the bolt to go into battery, either by depressing the

bolt catch or by pulling the charging handle slightly back towards the rear and then

releasing.

9. Ensure that the carbine is unloaded, place the muzzle in a safe direction and pull the

trigger to ease the tension on the trigger spring.

10. Place the selector lever back on “Safe” and snap the dust cover into position over the

ejection port.

NOTE: If a properly assembled carbine (MR556A1 Upper Receiver Kit and non-HK

lower receiver) fails to fire, or does not fire reliably, the cause could be the hammer in

the lower receiver. HK recommends a MIL-SPEC hammer be used with the MR556A1

Upper Receiver Kit. For further information, please contact HK Customer Service.

NEED HELP? If you need help installing or removing an HK MR556A1 Upper Receiver

Kit (URK) from a legacy AR-style carbine, please contact HK Customer Service at

TEL: 706-568-1906, EMAIL: [email protected]

HKDCS 011720