I went back to the Heller decision. Here is the relevant section from the courts opinion. In fact it appears in the SYLLABUS. Not being a lawyer I take this to be a summary (somewhere I remember it being said that it is not even written by the justices). Therefore it mustn't have the weight of the main opinion. Nowhere does the opinion say in certain terms that machineguns are dangerous and unusual. The ATF is making this connection through the references to Miller and English law. Boy talk about how a bureaucrat can twist words...
2. Like most rights, the Second Amendment right is not unlimited.
It is not a right to keep and carry any weapon whatsoever in any
manner whatsoever and for whatever purpose: For example, concealed
weapons prohibitions have been upheld under the Amendment
or state analogues. The Court’s opinion should not be taken to cast
doubt on longstanding prohibitions on the possession of firearms by
felons and the mentally ill, or laws forbidding the carrying of firearms
in sensitive places such as schools and government buildings, or
laws imposing conditions and qualifications on the commercial sale of
arms. Miller’s holding that the sorts of weapons protected are those
“in common use at the time” finds support in the historical tradition
of prohibiting the carrying of dangerous and unusual weapons.
Pp. 54–56.
Let me modify a bit what I said above...Looking at the referenced section of the opinion it does raise the issue of prohibited weapons commoning out of Miller. But it summaries that section of historical reference with this great line...
But the fact that modern developments have limited
the degree of fit between the prefatory clause and the
protected right cannot change our interpretation of the
right.
My read of that line basically says go pound salt to the government brief !!! I see it as "even though weapons technology has changed, the people still have a right to keep and bear it".