Disclaimer - the examples and figures I am using are purely hypothetical and NOT meant to be exact or accurate. This is just the theory
Originally Posted by Savage308
Forgive my ignorance but can you explain "recticle hold over vs twisting turrets for elevation adjustment"
When you "zero" the scope you are adjusting the point of aim (POA) to match the point of impact (POI). That point is only coincidental for one distance, say 50 yds (typical for a .22), any target that is closer or farther will cause the point of impact to shift (the moment the bullet leaves the barrel gravity takes over) the amount of shift will vary based on the specific ballistics of the ammo. If you only shoot one distance this is no big deal but if you engage mutiple targets at various ranges this can be an issue. I whipped up a diagram that might help.
As above, let's say you are zero'd at 50 yds but need to hit a target 100 yds away. If you don't make an adjustment and simply aim at the bullseye your shot will hit low (green line). In order to hit the target in the bullseye you can shift where you are aiming, or "hold over" the intended POI (purple line).
The only way to have the POA and POI match is to change the zero to correct for distance or "twist the turrets". When you know how much you need to adjust for a distance (data from a ballistics chart) you make the appropriate change (it is really incorrect to refer to the adjustment as "clicks" but many do) in MOA or MILS. In this case I have said you need 1.6 MILs at 100 yds and 3.3 at 150 yds. With the duplex reticle you are "guessing" at how much holdover you have, the mil-dot reticle allows precise holdover and adjusting the knobs allows you to hit where you aim.
Many shooters have no problem guesstimating and holding high but others want to have the bullet hit the spot where the crosshairs meet.
Adjustments are really only practical when the scope's adjusting turrets/knobs/dials are designed to be adjusted on the fly. Many hunting scopes are not setup with finger adjustable knobs since frequently there is not time when the animal is spotted and holdover/under is required. All most all tactical or longrange scopes are equipped to make frequent and precise changes by hand so the POA and POI always match.
Look at Leupold scope adjustment style
page. At the top you see the dials that are not really meant to be adjusted in the field (but can be) and as you move down you see finger adjustable dials and knob or turrets. Also note the amount of adjustment, some are 1/2 MOA per "click" others are 1/4 or even 1/8 MOA. At 100 yds 1 MOA is approximately 1 inch (actually 1.047") so you can see that it would take a lot of twisting (or clicks) with a 1/8 dial/knob to move 1 inch in POI but it would also provide very fine adjustment for a precise zero. Other complany make dials/knobs in that move the POI in values of inches ... 1/4 inch or 1/2 inch etc or as in my diagram, Milliradians or "MILs"