Here's the way that you set up the sights on an M1/M14 rifle (assuming they are all U.S. G.I. parts).
1. Center the windage marks on the receiver and sight base using the windage knob.
2. Crank the elevation knob so the aperture goes all the way up. With thumb pressure, try to push it down. If it goes down, tighten the screw in the windage knob (right knob, viewed from the rear) one half revolution clockwise.
3. Crank the aperture all the way up and try to push it down again. If it goes down, tighten the windage knob screw another half turn and repeat. If it does not, the sight tension is correct.
4. Crank the aperture all the way down and then bring it up 8 to 12 clicks. This should get an approximate 250 yard zero at 25 or 100 yards.
5. Calibrate the elevation knob. Loosen the screw in the left knob. Rotate the knob until the mark on the knob's scale is midway between the 2 and 3 marks (equals 250 yards) with the scribed mark on the ear of the receiver.
6. The mechanical zero is now set. Verify the setting by actual firing and then adjust the setting of the elevation knob as in 5. M1 Garand sights are calibrated in yards; M14 sights are calibrated in meters. The procedure for zeroing are the same for both.
It is not a good idea to retrofit your rifle with locking bar sights used by WW2 M1 rifles. You will have to replace both the windage and elevation knobs. The locking bar itself must be staked by spreading the end of the elevation knob shaft with a punch. You can only remove and replace the locking bar once after installation because of the staking requirement. On the second removal, the end of the elevation knob shaft is so damaged that the whole assembly must be replaced.
I have had an M1 with the old locking bar. It refused to hold elevation no matter what I did. I replaced it with the post-WW2 design and my problems went away. I repeat, do NOT retrofit your rifle with the old locking bar sight.
