The FBI has taken the position that it will not allow you to appeal you FBI background check and denial for an NFA Transaction. Yes, the FBI conduct the background check, denies you, and provides the NTN number for your denial, but... no appeal for you! I didn't believe it until I saw the document. I'm not sure how this is legal or proper, but we are looking into it. To see the actual letter, click here.
So basically, the FBI is denying you based on its database, and then wholesale refuses to allow you to appeal it. Smells like a due process violation.