End of year ruminations from David Codrea.

A core problem is that ATF has never followed the Administrative Procedure Act, 5 USC 522. That statute provides for three levels of disclosure.
“[S]ubstantive rules of general applicability … and statements of general policy or interpretations of general applicability formulated and adopted by the agency” are to be published in the Federal Register, from which they are edited into the Code of Federal Regulations. “An AR-15 receiver becomes a receiver and thus a firearm when the area that holds the fire control group is milled out” would plainly fit here.
“Final opinions, … as well as orders, made in the adjudication of cases” are to be made available for public inspection online. This would include rulings that a particular item is or is not a receiver, plus FFL revocations, and other such rulings.
Everything else is subject to disclosure, on request, through FOIA. The first two categories are not matter disclosed if requisition, they are supposed to be actively disclosed, and so is any amendment to them. ATF instead, if someone violates their unpublished standards, simply sends an official to testify that “we take the position” that X is true or this is a receiver, etc. That’s a clear APA violation.