They also did this about thirty years ago when some enterprising individual made a non-attached stock for a handgun. The item fit from the wrist of the hand to the shoulder.
As the Popiel Pocket Fisherman used to say, “And it really really works!” That’s why it was banned.
Nothing on earth pursues legalisms like the deep state, fourth branch of government. After all, to them, its the letter not the spirit of a law that matters.