Greg, the 80% lowers are legal if you complete the machining yourself and use it to assemble a firearm for your own use. As long as you retain ownership of it it is legal. It doesn't even have to have a serial number! If you want to transfer it to another person I believe you have to engrave your name, location and a serial number on it and submit a form to the ATF, much like you do when you manufacture an SBR. I am not positive on that last part but that is the way I understand it. Shibi might be able to say for sure since he has a manufacturer's license.