(1) The Telescopic Sight M73B1 (Weaver No. 330 C) used on the Rifle M1903A4 is set at zero windage and 100 yards elevation (when issued) as explained in TM 9-270. The mount base is alined and leveled by means of shims of proper thickness placed between mount base and receiver at manufacture. The position of the telescopic sight is fixed at the front end by the engagement of the mounting lug on the front mount ring (assembled to tube of sight) engaging in the mounting recess in the front end of the mount base. The rear end of the sight can be swung to right or left and then locked in position by movement of the lateral adjusting screws threaded into the mount base and bearing on the lug on the rear mount ring. The position of the rear end of the sight is fixed at manufacture by staking the left lateral adjusting screw in position. This screw should not be removed nor shifted except for repair or realinement of the sight when necessary. The sight is removed from the mount base by removing the right lateral adjusting screw and swinging the rear (eyepiece) end of the sight out from the receiver (bolt handle side) until sight is at right angles to receiver. Then lift sight straight up as explained in paragraph 7 a.
(2) However, if the sight gets out of line with the base and hence the bore, by shifting or removal of the left lateral adjusting screw or replacement of rings or mount base, it must be lined up again by bore sighting the rifle as explained below, and the left lateral adjusting screw then securely staked in place. By alining the sight with the bore, with the cross hairs (reticle) at zero windage (TM 9-270), maximum adjustment of the cross hairs is retained for windage adjustment by means of the windage adjusting screw. The same principle applies to elevation when the mount base is leveled at manufacture. If mount base is removed or replaced, the sight should be checked for vertical aiitiement with the bore in a similar manner. In such a case, the mount base can be tipped by placing the shim of proper thickness under the front or rear end of the mount base, as may be required. The horizontal cross hair should then pass through the point of aim. Before bore sighting, the sight should be adjusted for zero windage and minimum range of 100 yards as explained in TM 9-270.
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