After the debate Over selling/registering/marking receivers, I shot an email to the ATF. Here is there response.
Thank you for your recent inquiry to the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF). This is in response to your email in which you inquired about making a firearm.
Firearms may be lawfully made by persons who do not hold a manufacturer's license under the GCA provided they are NOT FOR SALE OR DISTRIBUTION and the maker is NOT PROHIBITED from receiving or possessing firearms.
In addition, the making of an NFA firearm requires a tax payment and advance approval by ATF. An application to make a machinegun will not be approved unless documentation is submitted showing that the firearm is being made for the official use of a Federal, State or local government agency (18 U.S.C. § 922(o),(r); 26 U.S.C. § 5822; 27 CFR §§ 478.39, 479.62, and 479.105). Please be certain that you adhere to the definition of "pistol" provided below to ensure that you are not making an NFA firearm, which would require registration and the tax stamp.
Additionally, although markings are not required on firearms manufactured for personal use (excluding NFA firearms), owners are recommended to conspicuously place or engrave a serial number and / or other marks of identification to aid in investigation or recovery by State or local law enforcement officials in the event of a theft or loss of the privately owned firearm.
There may be State laws that pertain to your questions. ATF has no jurisdiction over State laws. You need to contact your State's Attorney General's Office (a list of their offices is available online at
www.naag.org) to inquire about firearms laws and possible restrictions in your State.
Should you have additional questions, please contact your local ATF office. A listing of ATF office phone numbers can be found at:
http://www.atf.gov/content/contact-us/local-atf-office.
Regards,
David
Firearms Industry Programs Branch, ATF