1
Mojician
Re the .410 pistols, I believe the legal difference is the rifling in the barrel. A pistol chambered in .410 will also chamber and shoot .45 Long Colt which is a traditional pistol cartridge. They are not considered shotguns. If you were to shorten a shotgun and attempt to make a pistol out of it, it would still have a smooth bore, therefor it would still be a shotgun.
As I understand it the barrel determines shotgun from rifle and pistol, not the cartridge chambering.
Matthew