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 280 of 775
TM 9--2350--311--10
2--182
Change 6
2--12 PREPARATION FOR FIRING — CONTINUED
2--12.2
Boresighting — Continued
d. Checking Boresight of M117/M117A2 Panoramic Telescope Using the M140/M140A1 Alinement Device
— Continued
7
To ensure M117/M117A2 panoramic telescope (18), M145/M145A1 telescope mount (12), and
M140/M140A1 alinement device (27) are properly alined, the following additional check should be
made.
(a)
Rotate pitch level knob (35) and cross-level mechanism knob (34) of M145/M145A1 telescope
mount (12) in a clockwise direction.
(b)
Positions of pitch level knob (35) and cross-level mechanism knob (34) will be correct when upper
end of gear sector driven by pitch level knob and right end cross-level mechanism knob are in
“nearest to flush position” with respect to adjacent casting.
(c)
If M145/M145A1 telescope mount (12) is not in correct alinement, there will be excessive cutoff
when viewing M140/M140A1 alinement device (27) through M117/M117A2 panoramic telescope
(18).
8
Aline M117/M117A2 panoramic telescope (18) reticle crosshairs with M140/M140A1 alinement device
(27) using M117/M117A2 panoramic telescope azimuth knob (16) and elevation knob (17).
9
With M117/M117A2 panoramic telescope (18) reticle alined with M140/M140A1 alinement device (27),
pitch level knob (35) and cross-level mechanism knob (34) scribed lines alined, azimuth counter (19)
should read 3200 mils.
10
If azimuth counter (19) reading is 3200 mils
±
0.5 mil, weapon is boresighted. If not, conduct
M140/M140A1 alinement device (27) comparison tests (para 2--12.2f.). If, after verifying accuracy of the
M140/M140A1 alinement device, the M117/M117A2 panoramic telescope (18) azimuth counter (19)
exceeds
±
0.5-mil tolerance, boresighting must be conducted using test target method (para 2--12.2b.)
or distant aiming point (DAP) method (para 2--12.2g.) before the weapon can be fired.
NOTE
Breech is completely closed when witness marks on breech ring and breechblock aline.
11
If necessary, open breech and close completely.
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