Parallax is a tricky thing and i think that it is very poorly understood in the shooting community for as much as we use it.
1) Parallax is the adjustment to put both the reticle and target on the same focal plane (in focus together)
2) scope shaddow does not cause missed shots. bad form and parallax error cause dropped shots.
3) what is parllax error? Parallax error is the result of the target and reticle not being on the same focal plane. Maximum parallax error is when you peak through the edge of your scope to see the target and reticle while they are not on the same focal plane (50% scope shaddow)(nobody does this).
4) if you have perfect eye, sight, and target alignment. You have no parralax error and thus will never drop a shot due to parallax error. Even if you are shooting 1000 yards and your paralax is adjusted to 25
5) using a parallax error calculator to identify the max possible effect of parallax error you will see that if you set the scope parallax to 100yds and then peek though the top of your scope at a target set at 1000yds (acheiving max parallax error) your reticle will be .276 mills off of center. Keeping in mind that you likely arent shooting with 50% scope shadow or maximum parralax error. If you set your parralax to 500yds your max error from 100-1000 yards will never be greater than .245 mils
6) so what im getting at with all of this is that parallax really doesnt matter. If you adjust it so that you are close to the range the max error that you could experience is so small and unlikely that it simply will not effect you. I set my parallax to an average range between targets or at the furthest target so that it is the most clear when i take my shots and the closer targets will appear slightly bigger becuase they are closer.
Sorry for the very technical answer to a very simple question.
This quick calculator shows the amount of parallax error that may occur using a fixed-parallax scope to sight onto an object placed at a known distance.
www.lelandwest.com
