You build the gun then send in the Form 2. It is to tell ATF what you have built. You will get a copy back, even if you dont get a copy back who cares. It is your responsibility to fill out the form and send it in. You are not resposible to make sure they get it and enter it into the system. I send my Form 2s in by the USPS first class mail the same way ATF sends a copy back.