From the ATF website:
The Bureau of Alcohol, Tobacco, Firearms and Explosives cannot respond to e-mail inquiries relating to technical, policy and/or legal questions. Inquiries of this nature can only be addressed through a letter outlining your questions to the following address:
Bureau of Alcohol, Tobacco, Firearms and Explosives
Office of Public and Governmental Affairs
99 New York Ave. NE
Mail Stop 5S144
Washington, DC 20226
Question 1: What, if any, restrictions apply to transferring weapons that were built by a non-licensed individual for private use to other individuals?
Example: I built a firearm which conforms to the definition of a rifle, I now no longer wish to own this rifle, it is marked clearly per ATF guidelines with all required information. May I sell this firearm to another individual? May I transfer ownership of the firearm without selling it?
Is there a limit to the number of firearms that I may dispose of this way?
Example: I have a number of privately built firearms but no longer wish to maintain my collection. Is there a limit to the number of firearms that I may dispose of?
Is there a limit to the number of firearms that were built for private use that may be bequeathed to family members at the time of my death?
If for some reason in the future I were prohibited from owning these firearms could I legally transfer all of them to a family member or family members of my choosing?
Good luck with your questions.