If I'm going to shoot long distances with my AR and variable power scope, I have to open up the KAC Bulletflight App on my Iphone. This program is just awesome and takes all the guesswork out of hold offs and windage correction. There are three versions from the "Light" version ($3.99) to the full-on military grade version ($29.99). You can get really fancy with this program if you want: even taking into account things such as the Earth's rotation, wind, ballistic coefficients, etc. But I use it in a fairly simple manner. You can use one of the preset ammunition entries that come installed (such as 55g M193, 62g M855), or you can enter your own ballistics info for whatever load you are shooting. Then enter the type of click correction your scope uses, and let BulletFlight do the rest. I have a preset for my Leupold 3x9 Vari-X scope using M193. My scope is zeroed for 100 yards, and then I simply select my shooting distance in Bulletflight and it tells me the number of clicks to change my elevation. It really could not be simpler.
HERE is some old video of me using the app to shoot steel at long range.
Be safe and see you next time.