I would like to see the agent in that video convert one and then, without anything other than standard eye and ear protection, fire it. First he will have to figure out which way the magazine goes in.
Hey, don't discount the ability of the ATF Magic Machine Shop to convert anything into a machine gun. They could turn a stapler into an illegal, unregistered machine gun if they wanted. And even if they did this by simply duct-taping one to the top of a legal, registered machine gun, who is a federal judge going to believe?