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.
Bob Brister's more modern version of this involved his wife towing a target sled behind the family station wagon while he shot various loads at it from various distances, and compared to stationary patterns shot with the same loads at the same distances. String isn't a huge factor at skeet distances, nor at the distances most upland birds are shot. Much bigger factor for the really long range stuff. However, if you're talking waterfowling, that's a different story entirely because while a lot of waterfowlers would rather shoot lead than steel, one advantage steel does have is that it reduces string significantly.
