Stan: Mr Griffith thought a "cartwheel" pattern could be produced by an inadvertent groove in the bore that could caused the shot charge to spin
https://books.google.com/books?id=inQCAAAAYAAJ&pg=PA237
Back in my young and dumb days I cut an Invector extended rifled tube to 1" to make a magic skeet choke. The pattern was terrible frown

Folks have been trying to figure out shotgun patterns for a long time wink
http://books.google.com/books?id=inQCAAAAYAAJ&pg=PA49