I make my own "ballistic" turrets with an excel spreadsheet and a waterproof label paper. Took me a bit to craft the spreadsheet (formulas, formatting, reliable printing techniques) but it works really well and I have verified labels for different conditions to 1000 yards or so multiple times. I use it for hunting in lots of different altitudes, temps, etc. I really like what el matador said about zero at 500. Zeroing at the greater distance makes you margins of error smaller at closer ranges...brilliant. I love that a little technique can compensate for variance easily.