Helpful info
http://www.recguns.com/Sources/IIF1.html
You may only own a machine gun that was manufactured and registered with the BATF before May 19, 1986. Weapons manufactured after that date are restricted for Military and Law Enforcement use only.
So YES you are correct, however having a class 3 doesn't mean you can just go out and start picking up weapons left and right, as stated before and even someone else mentioned it, you gotta register and all that jazz so the local law enforcement can keep tabs on the weapons.