Robb your buddy did a good job but he forgot a point.
#4, angle of departure of said varmint.
I have also found that if you are shooting a round capable of achieving velocities near 4000fps it simplifies things considerably.
My personal rule with such a setup is that if they are anywhere under 100 no matter the angle of departure nor the speed at which they are doing their departing ,I always pull on FUR.
After about 150 then things start getting dicey again . Unless they are running straight away and then I will take a poke on out to around 300 yards by just pulling on their bunger and letting it rip.
After about 150 to 200 I figure if they have made it that far then they have won the day.
That is unless I have a personal gripe against said vermint, such as a calf or sheep getter.
In that instance I keep lead flying until he gets out of sight or I run out of bullets!
More than once I have watched the last bullet in my rifle send one ass over teakettle at ranges I surprised myself with.
