(1) The parallax of the Telescopic Sight M73B1 (Weaver No. 330 C) is adjusted by backward and forward movement of the reticle (cross hairs) attached to the adjustment plate on the sight. Parallax is adjusted at manufacture for 25 yards and beyond, and the plate screwed firmly in place. The plate should never be moved nor the screws allowed to become loose except when adjustment is found to be necessary. If parallax develops, it will cause the cross hairs to become blurred when the target image is in sharp focus. If no parallax exists the cross hairs should be clearly defined when the sight is rear mount/ .
ring r adjustment plate
, elevation screw
' locking spring locking ring
ring r adjustment plate
Figure 67 - Telescopic Sight M73B1 (Weaver No. 330 C) — Rear Section 5howmg Adjusting Screws and Eyepiece focussed on an object at 25 yards or more distant as described in TM 9-270. However as such a short range is not generally necessary, parallax should not be adjusted if correct for ranges used.
NOTE: The reiicJe in the Telescopic Sight M73B1 (Weaver No. 330 C) consists of a metal ring in which two very fine wires are assembled These wires cross each other at a right angle and are referred to as the "cross hairs." The reticle is assembled in the sight tube and adjusted by the windage and elevation screws as explained in TM 9-270.
b. Testing for Parallax.
(1) Place the sight on a rigid support, focus the sight, and aline the reticle (cross hairs) on a mark about 100 yards distant
(2) While looking through the sight, move the head from side to side. If there is any apparent movement between the reticle (cross hairs) and the mark, parallax is present.
(3) In the Telescopic Sight M73B1 (Weaver, No. 330 C), parallax may be present at 25 yards or less and not at greater distances If not present at ranges used, do not adjust.
c. Adjusting for Parallax. To eliminate parallax, proceed as follows:
(1) Lightly loosen the four screws holding the adjustment plate
(2) Slide the adjustment plate forward and back until the reticle (cross hairs) and mark sighted on appear stationary when the head is moved from side to side.
(3) Tighten the adjustment plate by turning down the screws securely.
CAUTION: Be sure the adjustment plate is moved backward or forward only and not laterally. If moved laterally, the vertical and horizontal alinement of the reticle will become shifted Do not remove the adjustment plate from the sight tube as the cross hairs in the reticle are very delicate and easily broken, and foreign matter may enter the sight tube. Loosen adjustment plate screws only enough to shift plate, else the curved nuts into which they thread may drop off inside the tube. This applies particularly to single (rear) screw, as nut may turn and break cross hairs.
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