Heckler&Koch MR762A1 - Manual (Page 17)

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d. Ensure that the hammer is in the down (cocked) position before attempting to install
the buffer and action spring. Mount the action spring onto the buffer and insert the
buffer and spring into the receiver extension. Push back on the buffer far enough
until the buffer is retained by the spring loaded buffer detent (Fig. 53).
2. Upper Receiver:
a. Install the gas piston into the back of the gas block. The piston rings need not be
staggered prior to installation (Fig. 54).
Fig. 54 – Reinstalling the Gas Piston and the Piston Rod
b. Insert the rear of the piston rod into the bushing located at the front of the upper
receiver above the barrel nut, compress the spring, and install the front tip of the
piston rod into the rear of the gas piston.
c. Slide the Free Floating Rail System (FFRS-handguard) onto the barrel nut, ensuring
that the tongue on the FFRS mounts into the groove on top of the upper receiver.
Once the FFRS is flush with the upper receiver, drift in the captive FFRS retaining
screw. Insert a 5mm hex wrench into the retaining screws and rotate clockwise until
hand tight.
Fig. 55 – Reinstalling the FFRS handguard
3. Bolt Assembly:
Fig. 56 – Bolt Assembly viewed from bolt face
Fig. 57 – Bolt Assembly components
a. Slide the bolt head into the bolt carrier until the circular mounting surface for the
cam pin on the bolt heads aligns with the front of the raceway on the bolt head
carrier. Pointed down range, the extractor should be on the right hand side of the
bolt carrier and ejector should be on the left (Fig. 58).
Fig. 58 – Bolt Carrier reassembly
NOTE: The bolt head on the MR762A1 features a tapered mounting surface for the
cam pin. This feature ensures that the bolt must be properly positioned in the bolt
carrier before attempting to install the cam pin.