Once the Form 4 etc is all complete, do you just mail them to the NFA branch office of the ATF?
Currently that address is
244 Needy Road
Martinsburg, West Virginia 25405
according to this page: https://www.atf.gov/content/contact-us/contact-ATF-service-centers
Currently that address is
244 Needy Road
Martinsburg, West Virginia 25405
according to this page: https://www.atf.gov/content/contact-us/contact-ATF-service-centers