Useful Forms

ATF form1 application (used when making an NFA item such as an SBR or suppressor for your own use)

https://www.atf.gov/firearms/docs/form/form-1-application-make-and-register-firearm-atf-form-53201/download

ATF form4 application (used when applying for a suppressor from an FFL)

https://www.atf.gov/file/61546/download