Link: The Volokh Conspiracy - -.
A 1951 law bans possession of automatic weapons, grenades, and explosives with the intent to commit high treason. A rather narrowly-tailored law, at first glance.
However, the law states that the President can by decree add "any other arms or ammunition" to the banned list. And any person with a banned weapon is presumed guilty of intending to commit high treason, and required to prove his innocence:
What a fascinating piece of lawyering. You can have weapons unless you intend to commit high treason, but if you have a weapon you're presumed guilty of intent to commit high treason. So the very act of carrying a weapon makes it illegal to carry a weapon. What a wonderful piece of circular logic.