CO, basically you can only assume that the scope is sighted in for 100(?) yards: all adjustments are made in ADDITIONAL 1/4 MOA, so if it's a 300 yard target, just adjust up that much MOA that your range card tells you to.
(and remember to multiply your 1/4 MOA clicks time 4).
Here's a not-so-short explanation of how to measure it out:
Use your "distance b/w mil-dots = 3.5MOA" method to see how many 10" long targets will fit inside your mil-dot distance. Let's say ~2.5 of them will fit inside your 3.5MOA space.
So that's 3.5/2.5 = [b]1.4 MOA for a 10" target[/b]. Since 1.4 MOA is 1.4" at 100 yards, you have to find out what range 1.4MOA covers 10".
So 10/1.4 = 7.15 (* 100 yards) = [b]715 yards[/b].
For windage, here's the way SWAT adjusts there approximate windage:
15mph wind is about a 90 degree waving flag. So take whatever approximate angle flag you have (say ~30 degrees), divide it by 90 (30/90 = 1/3), and times that by 15 (15 * 1/3 = [b]5mph wind[/b]).
When your range card says, let's say at 700 yards, to adjust for 4" of 1-mph wind, multiply that 4" times your actual wind (4" x 5mph = 20). Now multiply that times 4, since all windage adjustments are made in 1/4 MOA (25 x 4 = [b]100clicks[/b]). Finally, since 1 MOA is 1" at 100 yards, but covers a 7" distance at 700 yards, you have to divide that by your "actual range" to "100 yard range" distance-ratio (100clicks / 7 = [b]14.25, or 14 clicks[/b]). It's all a bit confusing at first, but it comes naturally after a while.
Jewbroni~