I had M1 turrets put on my 3 x 9 at Leupold. I shot it in 0 at 100, loosend allen screw and turned knob to 0 but there are still 7 horizontal lines showing above the base. I assumed I would be able to loosen screw, turn untill all lines disappeared and on zero then retighten screw.
Those are called base lines (BL) and are used for reference. For example: when we zero our 50cal M107's and slip the scales (zero the turrets) we usually have a base line of 2 or 3. For this example we will use a BL of 2 as initial zero. If I were to take a shot at 1000 I would need about 20 MOA of adjustment from my original zero at 500. My spotter would look at the data book for that rifle and tell me to go to BL3+5. M1 turrets have 15 MOA of adjustment per revolution, so this is one complete turn plus the additional 5 MOA needed. After the shot I can return to my original zero by just turning the turret till it is on BL2 and 0. They are also good to make sure the scope hasn't been adjusted accidentally in the field, in case I need to take a quicker shot using the reticle for hold over/ hold off/ leads.
I'm shooting a 300 BLK with 240 grain bullet and need approx 25 clicks from 100 to 250. Is their any way to set it so I don't have to count backwards from my 250 zero to get to my 100 yd zero with these turrets?