Full auto weapons are not actually illegal. many States will allow you to get a federal permit to own one. All semi auto's at least know require a very good knowledge of the gun plus some extensive machining to covert to reliable full auto operation. The BATF checkes out every design before it is allowed to enter the US or be made in the US "legally".
NFA/Class 3 weapons are actually relatively easy to get if you have the money and no criminal background. The standard way to get one is to have your class 3 dealer fill out a form 4. A copy of this must be signed by your "local law enforcement" which usually means police chief or sheriff. Then you send in your form 4 with a picture, finger print card and $200 tax check. Voila! You can now pay $13,000+ for your full auto M-16.
Class 3 weapons include machine guns, suppressors (silencers to non gun people) and short barreled long guns (short barrel being anything under 16 inches). Machine guns can only be transferred if they were made before 1986(I think). This includes lightening links and drop in sears for AR-15s.
Now, if you can't get a local law enforcement signature because your local chief/sheriff is a dick then you can always create and LLC or trust and have the class 3 item transferred to the LLC or trust with no signature!
The biggest catch of owning a machine gun is that you have to buy one from someone else that was made before 1986 so... Just like old Busse's that they don't make anymore they are going to fetch a premium.
I can go into more detail if anyone wants.
