TM-9-2350-311-10 M109 Operator's Manual for M109A2, M109A3, M109A4 and M109A5 Download
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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.