Old thread, but even if your scope is second focal plane you can still mil your target. If your scope is second focal plane, set up a target ( cardboard works best ) at 100yrds and draw a line down the center. Take a ruler or tape measure and make a horizontal line ever 3.6 inches threw the vertical line, with a total of 4 horizontal lines. Line your cross hairs up with the bottom line on the target and adjust your magnification until the mil dots line up with the marks you made on the target. Once you do that and the mils line up, take some white out and mark it on your scope.. Or make a mental note.
That will allow you to mil your target with a 2nd focal plane scope.
If the target is 68in tall ( the average hight of a man ) multiply 68x 27.77 or 27.8, then divide that number by how many mils the target takes up.. That will give you your range.