The lead for a moving target has very little, to absolutely nothing, to do with the shot string. Time of flight for the pellets, speed of the moving target, distance to the target, angle of the target, environmental factors such as wind or intervening brush and finally the actual shooting method used determine the necessary lead. The two most basic mistakes made when shooting a fast mover with a shotgun is to look at the bead instead of maintaining a hard focus on the target and for the shooter to not have their head down on the stock in a solid and consistent mount. Look at the bead and the shooter will slow or stop the swing - guarantee a miss. A consistent and solid mount with the head on the stock is referred to as having "the Rock on the stock." Float the eye above the rib inconsistently and it's another guaranteed miss.
