Simply looking at two dimensional patterns ignores the three dimensional aspects of a shot string. Greener's book has a wonderful section on dragging a long paper target on a rolling trolley to estimate the length of the shot string in 1910 technology. I've since since other writers use modern photography to illustrate it. While a gap or hole in the 2-d pattern is certainly proof of an identical hole in the 3-d pattern, the converse is not true, i.e. a "no hole" in 2-d cannot be assumed to be proof of "no hole" in 3-d--the pellets may have arrived at completely different times. Somebody probably has more current info on this factor than I do. Just food for thought.