MIL-DTL-48559 Mount, Telescope And Quadrant - M172A1This specification covers the Mount, Telescope and Quadrant: M172A1 which supports the Fire Control Quadrant: M18A1 for use on the M777 and M198 series of howitzers and gives elevation compensation to correct for cant when the mount is leveled by a cross level movement. The mount also supports and aligns the mounting bracket for the Elbow Telescope: M138A1.

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MIL-DTL-48559B

3.5.2 Locating keys for M18A1 quadrant. The locating keys for the quadrant shall

be parallel to the locating keyway in the mount mounting surface within 2 minutes of arc

(0.6 mil).

3.5.3 Mounting surfaces for gunner's quadrant. The mounting surfaces for the

gunner's quadrant shall be parallel to the keyway in the mount mounting surface within 45

seconds of arc (0.225 mil).

3.6 Performance.

3.6.1 Cross level adjustment. The mount shall travel through an excursion of at

least 34 degrees to the left and 34 degrees to the right from the center position.

3.6.2 Backlash (cross level). Backlash in the cross level mechanism shall not

exceed 1.5 mils at any setting between 34 degrees to the left and 34 degrees to the right.

3.6.3 Boresight elevation adjustment. The boresight elevation adjustment shall

move a line of sight a minimum of 18 mils above and 18 mils below horizontal utilizing the

slot in bracket assembly 10554685 as a pivot point.

3.6.4 Boresight azimuth adjustment. The boresight azimuth adjustment shall move

a line of sight a minimum of 18 mils to the left and 18 mils to the right of a vertical plane

parallel to the mount's mounting surface.

3.7 Cross level knob torque. The running torque required to rotate the cross level

knob shall be within the limits of 4 to 12 inch pounds when checked at standard ambient

temperature of +60�F to +90�F. Starting torque shall not exceed 18 inch pounds when

checked at standard ambient temperature of +60�F to +90�F. When checked at the

operating temperature conditions of 3.4.2, the running and starting torque shall not exceed

30 inch pounds.

3.8 Boresight elevation adjustment screw torque. The running and starting torque

required to rotate the boresight elevation adjustment screw at standard ambient temperature

of +60�F to +90�F shall not exceed 11 inch pounds. When checked at the temperature

conditions specified in 3.4.2, the running and starting torque shall not exceed 27 inch

pounds.

3.9 Interchangeability.

3.9.1 Interchangeability of mounting surface for M18A1 quadrant. Any M18A1

quadrant that is within specification shall be able to be installed on the M172A1 mount.

3.9.2 Interchangeability of mounting surface of M172A1 mount. The M172A1

mount shall be able to be installed on the mounting surface of any howitzer that is within

specification.