Is it possible to build a "ghost" full auto AR 15? By that I mean take a 80% lower, machine it for full auto parts, install the correct parts and have a legal unregistered full auto AR 15?
I believe that you can legally own the components of a full auto build, but once you install the components on a firearm that convert it to a full auto configuration, you're instantly in violation of Federal law. You may remember when people were selling Sten Gun kits that required milling and assembly. The kits were legal to own and you could have the tubular receiver/frame milled, but if you assembled the parts into a firearm you were violating Federal law.
Although I've never owned one or fired a rifle with one installed, a bump-stock on an AR would seem to give you a near full-auto shooting experience legally.
BTW, the manufacturing cut-off date for legal to own full-autos and banned full-autos is May 19, 1986.