Is it possible to install a collapsible or A2 style buttstock on a .223 pistol?

Thinking of buying a .223 handgun and installing a butt stock. Wondering about the legality of said modification, and if it's even possible. Never owned one, but seen em at gun shows, gun shops, and on CTD. Doesn't make sense that it would be legal to install a butt stock on it as, correct me if i'm wrong, but owning a RIFLE of similar design with a barrel any shorter than 16.5in requires special permits/licenses... is this illegal, or just a loophole that I've never noticed? Because essentially, a .223 pistol + tactical butt stock = badass little AR15 styled SMG...