When Congress passes a complex law, it usually gives some executive department the authority to make the rules and regulations needed to enforce it. Sometimes the department or agency will make very lax rules, sometimes very rigid ones.
Since all Federal gun laws arise out of the taxing power and the interstate commerce clause of the Constitution, enforcement and rule-making authority is given to the Secretary of the Treasury, who in turn delegates it to the Bureau of Alcohol, Tobacco, and Firearms. All three of these general product areas involve taxes, which is why they are lumped together. (Firearms are taxed, but remember that a dealers' and manufacturers' "license fees", are really special occupational taxes, and that the Class III transfer money is really a transfer tax.)
BATF can make rules and regulations, and does, but cannot go beyond the law in doing so. If they do, a court decision will almost always go against them. Of course, they always have to take orders from the Secretary of the Treasury and he from the President, so the rules and regulations can be hard or soft, depending on the policy of the administration.
When the law allows an option (e.g., "The Secretary may permit...") the Secretary in one administration may "permit", and the Secretary in another administration may not "permit".
That is one of the reasons our votes will be so critical this election. If you don't vote, don't complain about what you get.
If the law appears to be wrong, we can work to change it; but complaining about BATF is silly when the law itself is the real issue, not the regulations.