So I watched the new Pierce Brosnan movie last night (Survivor), in it he is going to shoot the Times Square Ball (filled with explosive gas) on New Years, his scope bracketed the ball with 7mils, the ball is 12' diameter. You use the size of the target in yardsx1,000÷mils=range to target.
12'=3.636yrdsx1,000=3,636÷7 (mils)=519.42yrds
The ball did look huge in the scope.