Heckler&Koch MR556A1 User Manual

Page 18

f. While maintaining forward pressure on the back of the firing pin, drift the firing pin

retaining pin from left to right.

g. Ensure that the firing pin retaining pin is properly installed by pivoting upwards on the

firing pin safety while pushing backwards on the bolt head. The firing pin should be

retained inside the bolt carrier (Fig. 60).

Fig. 60 – Firing Pin Retaining Pin Installation

h. Turn the upper receiver upside down, insert the charging handle into the upper receiver,

align the lugs on the outsides of the charging handle with the recesses on the inside of

the upper receiver then press down until the charging handle is flush with the inside of

the receiver then press slightly forward (Fig. 61).

Fig. 62 – Charging Handle Installation

i.. With the upper receiver and charging handle upside down, install the bolt assembly

onto the bottom of the charging handle ensuring that the bolt carrier’s anvil and the

top of the cam pin are centered in the bottom cavity of the charging handle (Fig.63).

Fig. 63 – Installing the bolt assembly into the upper receiver

j. Push the charging handle and bolt group completely into the upper receiver until the

locking lugs on the bolt head engage the locking on the barrel extension and the latch

on the charging handle engages the oval locking surfaces on either the left or right

hand sides of the upper receiver. The latch can be mounted on either the left or the

right hand side of the charging handle (Fig. 64).

Fig. 64 – Completing installation of the bolt assembly into the upper receiver

4. Upper and Lower Receivers:

WARNING: Always use the Disassembly Tool to disengage the detents on both the

rear takedown pin and the front pivot pin. Attempting to install the pins without

disengaging the detents could lead to damage of the lower receiver.

a. Ensure that both the captive front pivot pin and rear takedown are drifted out to the

right hand side of the receiver. If necessary, use the small surface of the MR556A1

disassembly tool.

b. Place the upper receiver pointed downwards with the flash hider resting on a padded

surface.

c. Mount the lower receiver to the upper receiver. Drift the front pivot pin from right to

left. The pivot pin will not completely lock but it will engage the upper receiver (Fig.

65).