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 3-7 FIRE CONTROL ALINEMENT TESTS AND MEASUREMENTS — CONTINUED 3-7.3 Leveling Gun Trunnions NOTE Gun trunnions must be leveled to ensure the fire control equipment mounts are parallel with the cannon tube. There are two ways to level gun trunnions: plumbline method and scribed lines method. a. Plumbline Method 1 Attach crosshairs (1) made of fibrous twine (item 39, Appx D) at witness marks on muzzle brake (2). 2 Install breech bore sight (3) or remove firing pin and use firing pin hole for rear sight instead of breech bore sight. 3-86