Re: Full auto conversion
The only machine guns that a civilian can legally own are ones that were made and registered with the ATF prior to May 1986. This is due to the Hughes Amendment of the Firearms Owners Protection Act that went into effect at that time. The Hughes amendment effectively closed the NFA registry in regards to transferable machine guns. There are registered receivers, registered drop in auto sears, and registered lightning links for AR family firearms. All of which accomplish the same goal (Full auto) but by different means.
Any machine gun legally made after 1986 can only be transferred to a law enforcement agency or the military, or an FFL who is also a Special Occupational Tax (SOT) payer. The SOT would also be required to have a demo letter from a law enforcement agency.
I as an 07FFL/02SOT can make machine guns all day long, but I cannot transfer them to anyone other than those mentioned above.
I hope this helps. Let me know if I can answer any more specific questions.