Dave, the reference which I used is late gunwriter G. T. Garwood. He says that the rifling will be very low rate of twist but does not state a ratio. Stated goal a widely dispersed close-range pattern without the use of a spreader load; no mention of a multi-purpose use such as shot and slugs. Pellet deformation didn't occur to me as a mechanism for dispersion; although unstated I had assumed that the principle was centrifugal force in the shot engendered by the charge following the twist of the rifling. Garwood is quite clear about the French origin of the concept and its intended close range use on "stunt" fliers. The maker mentioned is Bretton so I am stretching a bit to suggest that the rifled shot barrel is common among other French makers. If "tw" happens along, he may be able to tell you more than I can.
jack
