Someone over on arfcom dug up the fact that the Hughes Amendment was defeated, not passed, and made into law anyway. Some information is in the machine gun ban section in http://en.wikipedia.org/wiki/Firearm_Owners_Protection_Act
The arfcom thread is at
http://www.ar15.com/forums/topic.html?b=1&f=5&t=1051358
The arfcom thread is at
http://www.ar15.com/forums/topic.html?b=1&f=5&t=1051358