I’ve got a small one shoots 1 inch lead balls and a couple of motors 1 shoots 303 vegetable can full of cement and other uses coke can full of cement! All use black powder for charge and can fuse ignition!
at what point (if any) would a tax stamp be required? or are they considered antiques/relics? for functional ones of course, non functional i dont guess there are really any issues- unless ya are unfortunate enough to have an HOA or some such....