Calibration of the aiming devices of the FH70 gun

Calibration of the FH70 gun

Quadrant Calibration

To perform the quadrant calibration, you need to:

Place the 155-mm self-propelled towed howitzer “FH-70” on a firm surface, lower its base plate, and raise the wheels.

FH70 Base Plate

FH-70 placed on the base plate (wheels raised)
Clean the control surfaces on the breech from dust and wipe them dry.

Set the quadrant to an angle of 0-00, place it on the control surface perpendicular to the barrel, and level the howitzer using the hydraulic system (raising the right or left trail).

Breech Control Surface

*Positioning the quadrant on the breech control surface*
Place the quadrant on the control surface along the barrel and, using the vertical aiming mechanism handwheel, adjust the bubble to the center (between the markings).

Rotate the quadrant 180°. If the bubble is exactly in the center, the quadrant is calibrated (acceptable error — no more than 1/4 of the quadrant vial scale division).

If the bubble has shifted, correct part of the error using the quadrant set screw, and the rest using the vertical aiming handwheel to center the bubble.

Repeat these actions until the bubble does not shift when the quadrant is rotated 180°.

Calibration of zero sight settings:

Set the quadrant angle to 0-00. Then, placing the quadrant on the control surfaces, level the howitzer barrel horizontally both longitudinally and transversely.

Next, place the quadrant on the panorama base edge parallel to the longitudinal level. Rotate the vertical aiming mechanism handwheel to center the bubble in the quadrant.

Turn the quadrant 90° on the panorama edge and center the bubble by rotating the transverse swing mechanism handle.

Then return the quadrant to the longitudinal level to check if the bubble deviated.

After all these actions, the sight scales should show zero settings, and the transverse level bubble should be exactly in the center.

If the zero markings on the sight mechanism scale do not align with the pointer line, loosen the six hex bolts securing the setting ring and rotate it until the zero marking aligns with the pointer line. After that, tighten the bolts again.

If the transverse level bubble is not centered, adjust its position using the upper and lower adjusting screws. First, remove the transverse level cover, which should be reinstalled after the adjustment.

Calibration of Zero Sight Settings

Process of calibrating zero settings of the sight:

Set the quadrant angle to 0-00 and successively place it on the control surfaces to level the barrel horizontally in both longitudinal and transverse directions.

Then attach the quadrant to the panorama base edge, positioning it parallel to the longitudinal level. Rotate the vertical aiming mechanism handwheel to center the bubble of the quadrant.

Quadrant Placement

*Positioning the quadrant on the panorama base edge parallel to the longitudinal level*
Rotate the quadrant on the panorama base edge by 90°, and by turning the transverse aiming mechanism handle, again center the bubble.

Reposition the quadrant parallel to the longitudinal level and verify that the bubble has not shifted.

After completing these operations, the sight scales should indicate zero settings, and the transverse level bubble should be exactly in the center.

If the sight scales do not align with the pointer line, loosen the six hex bolts securing the setting ring. Then rotate the ring so that the zero marking of the sight scale is aligned with the pointer line, and secure the bolts.

*Setting ring adjustment of the mechanical sight scale* Zero Mark of the FH70 Sight Scale

*Zero mark of the sight scale set against the pointer line*
If the transverse level bubble is not centered, adjust its position using the upper and lower adjusting screws. Remove the transverse level cover for this purpose, and replace it after adjustment.

Transverse Level Adjustment

*Transverse level adjustment*

Transverse Level Adjustmen

Calibration of zero aiming line by a distant point on the terrain:

Place the self-propelled howitzer “FH-70” on a firm surface, install the panoramic sight into the mount and secure it with the clamping screw.

Stretch the threads along the marks on the muzzle face.

FH70 Barrel *Stretched threads along the marks on the muzzle face*
Remove the firing pin from the breech block.

Align the hole in the breech block with the center of the thread cross on the muzzle face and aim the barrel at the aiming point (the distance to this point should be at least 1000 meters).

Barrel Aiming FH70 *Aiming the barrel at the target point through the breech block hole and the center of the thread cross on the muzzle face*
Level the sight using the transverse level and, by rotating the panoramic sight and azimuth drums, align the panorama cross (central aiming mark) with the point at which the barrel is aimed.

As a result of the aforementioned actions, the azimuth and reflector scales of the panoramic sight should indicate a setting of 0-00.

*Panorama aiming at target point*
If the azimuth and reflector settings deviate by more than half a division, loosen the bolts on the azimuth drum using a screwdriver. Rotate the azimuth ring with divisions so that the zero divisions align with the indicator marks, then tighten the bolts.