More than you think. The "sawed-off shotgun" style (actually the from-the-factory short-barreled no-stock large-caliber smooth-bore pistol) is actually the most accessible NFA ("Class III") firearm, being priced only a little more than a shotgun and needing only a $5 tax payment (plus a page of paperwork). They can be had legally.
Truly "sawed-off" shotguns require a $200 manufacturing tax (plus same paperwork).
Illegally "sawed-off" shotguns can cost the owner $250,000 and 10 years federal prison.
ctdonath2: More than you think.
Well I don't know how many more since my point, to someone else, was that a lot of FReepers do. Thank you for affirming it.
I also appreciate the info about legal, illegal and Class III shotguns but I think I'll stick to my legal sawed off Mossberg with after-market pistol grip. At least until I buy a folding stock. And yes it is literally sawed off not factory-short.