I have read the entire ATF regulations book but could not find anything that specified that a serial number must be on a home-built receiver. Manufacturers, of course, are required to do so. I found the section that says you can build your own receiver as long as you don't sell it. Anyone checked with ATF to get a definitive answer on this issue? Also, anyone checked to see if you can give a firearm away that you home-built? I understand the selling part as that makes you a manufacturer, but seems you should be able to give any home-builts to family or friends. If not, what about when you die? What must be done with the firearm? ATF's book is rather vague on this whole subject.