Heckler&Koch MR556A1 - Manual (Page 15)

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Fig. 44 – Loosening the FFRS screw with hex (Allen) wrench
b. Slide the Free Floating Rail System (FFRS) off the barrel nut and remove the FFRS
from the upper receiver.
c. Grasp the rear of the gas piston while pushing back on the piston rod. Disengage
the piston rod from the piston and slide out the piston rod from the upper receiver
(Fig. 45).
Fig. 45 – Removing Piston Rod
d. Slide the gas piston to the rear and remove the gas piston from the gas block (Fig.
46).
Fig. 46 – Removing Gas Piston
5. Lower Receiver:
NOTE: Always ensure the hammer is in the cocked position (down) before attempting
to remove the buffer and action spring.
a. Depress the buffer detent with the tip of the piston rod and remove the buffer and
action spring from the receiver extension (buffer tube) (Fig. 347).
Fig. 47 – Removing Buffer Assembly
b. Check to ensure that the buttstock tightening screw is loose before attempting
to remove the buttstock. If tight, insert the large tip (3mm hex) of the MR556A1
Disassembly Tool into the tightening screw and rotate (but do not completely
remove) counter clockwise (Fig. 48).
Fig. 48 – Buttstock Tightening Screw
c. To remove the buttstock, simultaneously depress the back of the buttstock release
lever while pulling downwards on the front lip. Slide the buttstock off the receiver
extension.
Fig. 49 – Removing Buttstock
The MR556A1 is now operator disassembled (field stripped).
NOTE: Disassembly beyond the above field stripping procedures should only be
undertaken by HK certified personnel.