Scott F,
Prairie dogs are indeed quite a bit bigger than ground squirrels, exactly how much bigger depending on the species of ground squirrel. But PD's are also a lot spookier, and the shooting ranges increase quickly after they've been shot at some. Wind is often harder in PD country as well, which increases the difficulty with range.
Have shot considerable numbers of both over the decades, in several states, and PD shooting is normally tougher, especially after they've been shot at for a day or two.
