I thought it may be helpful if we had a "resources" thread for NFA type stuff. Here is the 5320.8 NFA Handbook. Here is the 5320.1 "Form 1". Here is the 5320.4 "Form 4". Here is the 5330.20 "Certificate of Compliance." The definitions of NFA Firearms are available in NFA 5320.8 as well as the definitions of "Permanently attached Muzzle Device" and other need to know definitions. The forms are for you if you decide you want to buy an NFA firearm, or maybe make an NFA Firearm. As always, if you have any questions, I'd be happy to help you out.