A distinction without a difference. I need a Bill, a legally-drafted and signed Bill. Otherwise, nothing stops the Dems from banning all semis by 'an ATF rule'.
Agency rules are subject to review and must comply with the underlying statute. Not to worry. You can call a fork a spoon but when the definition is reviewed by a court, its still a fork.
Bump stocks are not worth a review by us or them.
The Heller decision stops the banning of all semi autos.