To perform steps a and b, remove one 5-mm capscrew from any part of the gun. If machine key does not seat, move breech assembly from side to side.

a. Install 5-mm capscrew (7) in machine key (8) three turns and insert machine key into receiver hole

b. Turn machine key (8) until it slides down and sets in breech slot. Remove capscrew and reinstall it in the part of the gun from which it was removed.

M242 Breech

c. Install new retaining ring (10) in groove inside receiver hole (9). Make sure retaining ring (10) is seated securely in groove.


a. Place auto gun receiver (1) with barrel lock pin hole (11) on top.

b. Install barrel lock pin (12) and helical spring (13) in barrel lock pin hole (11).

c. Compress helical spring (13) with drive punch and hold pin compressed throughout step d.


d. Install headed straight pin (14) through barrel lock pin hole (11), through the barrel lock pin (12) and over the compressed helical spring (13). The barrel lock pin (12) will need to be lifted slightly to align barrel lock pin hole (11) with hole in barrel lock pin (12).

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