Heckler&Koch MR556A1 - Manual (Page 28)

54 55
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