Oh, boy. johnchris, as a fellow librarian, please don’t take this as a putdown when I say that you desperately need to educate yourself on this. All of those parts are legal to buy off-the-shelf without a license; the part of a semiautomatic rifle that, legally, is the rifle (i.e. the thing that you need a special license in order to own) is called the lower receiver, and a working one can be and has been printed on a 3D printer. I think that you want to familiarize yourself on what they look like so that someone won’t just give you a file that’s labeled “Abstract Sculpture #117” and have you print it off.
