TM-9-2350-311-10
HOWITZER, MEDIUM, SELF-PROPELLED, 155MM; M109A2, M109A3, M109A4 AND M109A5
TECHNICAL MANUAL; OPERATOR’S MANUAL
NOVEMBER 1994
TM-9-2350-311-10 - Page 73 of 775
TM 9-2350-311-10
1-14 EQUIPMENT OPERATION AND DESCRIPTION — CONTINUED
1-14.8 Mount and Howitzer Assembly — Continued
b. Breech Assembly
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CHAMBER. The chamber (8) holds powder charge.
OPERATING HANDLE. The operating handle (9) is used to open the breech manually.
OPERATING CAM. The operating cam (10) permits automatic opening of the breech.
BREECHBLOCK ASSEMBLY. The breechblock (11) locks into place behind the chamber (8) holding the
powder charge. On closing, the breechblock threads engage with the threads of the breech ring (2).
When these threads are engaged, they lock the breechblock in place.
SPINDLE ASSEMBLY. The spindle assembly (12) seals the powder chamber to prevent escape of
gases into the cab.
VENT HOLE. The vent hole (13) directs the primer blast against the base of the powder charge.
PRIMER CHAMBER. The primer chamber (14) holds the primer in place for firing.
FIRING GROUP BLOCK. The firing group block (15) slides over the primer and positions the M35 firing
mechanism (on M185 cannon assembly) or M49 firing mechanism (on M284 cannon assembly) for firing.
1-35
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