Re: Shepherd scopes
It doesn't take a lot to figure it out. The circles are either 18" to match a whitetail chest or 24" for an elk chest if I recall correctly; you buy the scope accordingly. You can figure out the rest with a little quick, simple math. As far as the distances between circles, if one's too big and the other too small, they tell you to hold central between them. If you can tell it's a lot closer to one than the other, though, hold closer to that one. When it comes down to it, though, I think knowing a mil-dot reticle, front focal plane, and how your setup works on it is the better way to go. As a compromise, the Nikon BDC isn't bad once you figure out the subtensions of all the features at 100 yards. With that, you can do a decent amount of ranging, but again, know how your setup works with those circles.
The one big advantage I see with Shepherd, though, is the dual reticle. If one moves, you will know it. As for sighting in with one shot as they claim, that can be accomplished on any scope as long as you have something to hold it steady while you adjust.