I guess OOO buck makes more sense than OO which just seemed rather silly (why use a 0.3" ball in a 0.41" barrel?) but I wonder why nobody's come up with interesting 28ga shotguns with a fixed choke to 0.498"? I'm not sure the BATF would call a barrel with a fixed choke "rifled", so such guns might be limited by the 18"/26" restriction, but keeping the bore below 0.5" would avoid the "sporting purposes" restriction. I would think a bull-pup semi-auto shotgun could be configured to allow reasonably effective point-shooting from the hip (use stock adjustments to match point of aim to the shooter's expectation) while possessing excellent retention characteristics (only 6" or so in front of the grip, while a "fork" would be cradled in the shooter's forearm).
So this pistol doesn’t count as a “sawed off shotgun” because it has a rifled barrel? I don’t know how the regulations work here.