I have never done any long range work, but I just bought aColt 24" and will be trying my hand a long ranve varmint work.  My Brother -in-law has 120 acres with fox, coyote,groundhog and other problems and I have been invited to help him clean house.  

My question, what scope, how do you compensate for changing ranges?  I will be shooting from 150-600 m.  I am looking at 77 grain rounds (per a kind suggestion on the ar15 board.  He uses a Luepold varixIII 4.5-14 with turrets ( whatever they are).  Help me get the right scope and understand what to do with it.  Thanks in advance.  

if you can find a 6-24x for cheap youll have a lot of fun.