Calibrating the sighting devices of the 155 mm M109A3 self-propelled howitzer

Calibrating the quadrant

To calibrate the quadrant:

a) place the 155 mm M109A3 self-propelled howitzer on a hard surface;

b) set the quadrant to 0-00, place it on the leveling plate across the barrel and level the M109 using the jacks;

 Placing the quadrant on the breech leveling plate

c) place the quadrant on the leveling plate along the barrel and, using the elevation handwheel, bring the quadrant bubble to the middle (between the marks);

d) turn the quadrant through 180°. If the bubble stays exactly in the middle, the quadrant is calibrated (an error of no more than 1/4 of a division of the quadrant vial scale is permitted);

e) if the bubble moves, center it with the quadrant micrometer knob and read the setting;

f) half of the reading is the error correction (positive if the arm is set to zero, and negative if it is set to minus 10 mils);

g) record the error correction and apply it, with the correct sign, to all barrel elevation angles when laying with the quadrant.

Checking the sight zero settings

To check the sight zero settings::

a) set the sight to zero;

b) center the cross-level and longitudinal levels of the sight and the panoramic telescope

Cross-level and longitudinal levels of the sight and the panoramic telescope

c) set the quadrant to 0-00 and place it on the breech leveling plate along the barrel;

d) after these operations the quadrant bubble should be centered (between the marks);

e) if the quadrant bubble has moved, center it with the quadrant micrometer knob and determine the deviation

 Centering the quadrant bubble and determining the deviation

f) set a barrel elevation of 100 mils on the sight and, using the elevation handwheel, bring the longitudinal level bubble of the sight to the middle. Set the same angle on the quadrant and determine the deviation. Repeat the steps above at barrel elevations from 200 to 800 mils and calculate the average deviation;

g) enter the calculated average deviation into the correction mechanism

Average deviation entered in the correction mechanism

Checking the zero line of sight

To check the zero line of sight against a distant aiming point on the terrain:

a) place the M109 howitzer on a hard surface;

b) stretch threads across the marks on the muzzle face of the barrel

Threads stretched across the marks on the muzzle face of the barrel

c) remove the firing mechanism from the breech block;

d) aligning the hole in the breech block with the center of the thread cross on the muzzle face, lay the barrel on the aiming point (the distance to the aiming point must be at least 1,500 m)

Laying the barrel on the aiming point through the hole in the breech block and the center of the thread cross on the muzzle face

e) set the sight vertical using the cross-level and lay the panoramic telescope reticle on the point on which the barrel is laid

Laying the panoramic telescope on the aiming point

f) as a result of these operations the angle-measuring (upper) scale of the panoramic telescope should read 32-00

Angle 32-00 on the angle-measuring (upper) scale of the panoramic telescope

g) if after laying the panoramic telescope the angle on the angle-measuring (upper) scale is not 32-00, you must:

1) unscrew the protective cover of the panoramic telescope shaft lock

The protective cover of the panoramic telescope shaft lock unscrewed

2) press the panoramic telescope shaft lock with a screwdriver and, turning the azimuth handwheel, set 32-00 on the angle-measuring (upper) scale of the panoramic telescope

 Setting the angle 32-00 on the angle-measuring (upper) scale of the panoramic telescope

3) release the panoramic telescope shaft lock and screw the protective cover back on.

Also on this site

• Calibrating the sighting devices of the FH70 gun
• Orienting the panoramic sight to mils 64-00 using the PAB-2M aiming circle
• How to enter the correction when firing illuminating projectiles
• Why is it so important to fire at higher angles?
• Range tables for specific projectiles
• Mortar-style firing: the effect of traverse on accuracy
• Cognitive information — all articles of the section