Field artillery materiel

by Unknown

CARE AND INSPECTION OF SIGHTS.

Rear sight Bracket.—Should not be bent, broken or cracked. Must be seated firmly in the bracket support.

Shank Socket Mechanism.—Not bent or burred; interior of shank socket, scroll and worm gears free of scratches, burrs or deformed threads. Sight shank easily inserted and moved up and down in the socket. Scroll gear securely held in mesh with rack of sight shank. For large movements of shank, should be easily disengaged by pulling out scroll gear handle; must be securely held in place by spring when released. Keep interior well lubricated. See that level vials of cross and elevation levels are intact and bubbles not too large.

Sight Shank.—Rack on right side must engage with scroll gear; keep lightly oiled. Sight shank should remain in fixed position except when disengaged or operated by scroll gear handles. For changes in range of 300 yards or less use only the scroll gear; over 300 yards pull scroll gear handle and slide shank up or down in socket by hand, making accurate setting with the scroll gear.

Panoramic Sight.—Lug must fit snugly in T slot of rear sight and then held fast by clamp screw and ratchet. When making ready for march order, first set the azimuth and R & L deflection scales at zero, and the elevation scale at 300. Release clamp screw and ratchet. In removing panoramic sight, grasp at center below the azimuth gear case, lift vertically out of the socket, lower the top of sight to the left and replace in panoramic sight box.

Quadrant.—Must fit snugly in its bracket, spring catch engaging. Nut on range disk must be tight to prevent slipping. To remove quadrant, press on spring catch before sliding off bracket.

The sights are correctly adjusted when, at zero elevation and deflection, correction having also been made for difference of level of wheels, the line of sight is parallel to the axis of the bore.

The range quadrant is correctly adjusted when, with the range disk set at zero, level set at 300, axis of gun horizontal and corrected for difference of level of wheels, the bubble of the range level is centered.

In adjusting sights, the panoramic sight should first be corrected. If the rear sight is adjusted first, it will require readjustment if the subsequent adjustment of the panoramic sight causes a change in position of the rear-sight range strip.

To adjust the panoramic sight.—Select a well defined point at least 2000 yards distant. If the bore sights are not available, stretch two threads or hairs from the tail of a horse across the grooves marked on the face of the muzzle and fasten them by a strap or rubber band. Remove the firing-lock case from the hub of the block-carrier. By sighting through the hole in the vent bushing of the breechblock, adjust the intersection of the cross hairs on the distant point, using the elevating and traversing mechanisms of the gun. Now without moving the gun or disturbing the laying of the cross hairs, bring the cross wires of the panoramic sight on the same distant point by means of the azimuth scale worm-knob and the scroll gear of the rear sight (on panoramic sights, M1915, to the deflection R & L scale should first be made to read 0, and the elevation scale of the objective to read 300). The cross hairs of the gun and the cross wires of the panoramic sight will thus be laid on the same point. Now adjust the azimuth micrometer scale to read 0 by means of unscrewing and tightening the screw on the milled head. Loosen the nut on the range strip; move it up or down until it reads (0) 100. Tighten the nut again. Verify the laying. For this adjustment, it is not necessary to have the wheels or the carriage on a level platform; cross level should be leveled.

To adjust the rear sight.—Having adjusted the panoramic sight and the rear sight range strip as described above, and without disturbing the laying of the gun, shift the deflection scale of the peep sight and raise or lower the front sight until the cross wires of the latter are laid upon the same distant point. Now loosen the two screws of the deflection scale and place the 0 of this scale opposite the index of the peep sight. The front sight is raised or lowered by removing the split pins and then turning the front sight in the sight bracket sleeve either up or down.

To adjust the quadrant.—(a) If an adjusted B. C. telescope or another gun with its quadrant in proper adjustment is available, the angle of site of some distinctly visible and distant point is measured by either of these means. The gun to be adjusted is then laid upon this distant point either with the bore sights, or with the tangent sight set at 0 (or some other convenient) range. The measured angle of site is then set off on the level scale of the quadrant and the bubble of the range level is centered by turning the handwheel of the range disk. By using the quadrant wrench, the range disk is then adjusted to read 0 range, (or the convenient range previously set off on the tangent sight).

(b) If no means are at hand to correctly measure the angle of site of a distant point, the quadrants may be adjusted by using two guns as follows: Unlimber two guns at about the same level, first seeing that the sights are in adjustment (par. 75). Lay both guns upon some distant point by means of the panoramic sight set at 0 range. Now set both quadrants for the same angle of site (roughly estimated A. S. of the distant point) and center the bubbles of the range level by turning the handwheel of the range disks. By means of the quadrant wrench, adjust the range disk of one of the quadrants to agree with the other. Whatever error exists will now be the same in each quadrant.

Now move one of the guns about 100 yards away and turn the muzzles toward each other. With the sights set at 0 range, lay the panoramic sights upon each other and measure the angle of site of each gun. Half the difference of the two readings will be the slope of the line of sight between the two guns. On the level scale of the quadrant which read the greater angle of site, set off 300 plus the half-difference, on the other quadrant set off 300 minus the half-difference. Now center the bubble of the range level by turning the handwheel of the range disk. By using the quadrant wrench, adjust the range disk until it reads 0 range. Having thus adjusted two guns, the others may be adjusted by the first means described.