Yeah? Machine guns are still legal, mostly.
The National Firearms Act of the 30's required a Federal Tax Stamp for the transfer or sale of a machine gun. The Feds then refused to issue the stamp. They did the same with marijuana once the Supreme Court upheld the practice.
Some old ones are. New ones can't be made legal. And God forbid you should have a slam-fire on a semiautomatic while a BATFE agent is watching. Instant felony charges - because a part of a previously-legal gun wore out! I don't think I'd be so bold as to state that "machine guns are legal" - "some machine guns not entirely illegal" is closer to the truth.