Zak, I don't know if you are an expert on the legalities of Class III as opposed to a technical expert on Class III stuff, but here goes.
I think NFA 34 and the lone Supreme Court case that buttresses it, Miller 1939, is a legal house of cards that has never been blown to bits simply because no one has ever challenged them in court.
As I understand Miller '39, Miller was arrested and charged for transporting an NFA weapon, specifically a double barrelled shotgun, across a State line without having paid the $200 NFA "tax" on it.
The initial Federal Judge ruled in favor of Miller, effectively throwing NFA 34 under the bus, as a violation of Miller's 2nd Amendment rights.
When the case got to the Supreme court, only the Government's lawyers and the judges were there. There was no one there to argue the pro-Miller, pro-2nd Amendment, side of the case.
The government's case was that the lower court decision should be reversed because the specific arm in question, a sawed off shotgun, was not
suitable for militia use.
The Supreme court accepted that argument, thereby reversing the lower court decision and re-instating NFA 34 which remains in effect to this day.
However, if you take the government's own argument one step further, which the Miller court did not and no court since has not, any weapon that does
have a "militia use" should be
protected under the 2nd Amendment. In other words, by the government's own argument
the Class III stuff controlled under NFA 34 should not
be controlled under NFA 34!
If Miller had had, say, a BAR instead of a sawed-off shotgun, the government would not
have been able to make the "no militia use" argument and the lower court might have been sustained, and NFA 34 would have remained scrapped.
Am I wrong there?
Since then of course, we have had the 1986 "Ban" on production of new NFA weapons. If the combination of NFA 34 and the 1986 does not "infringe" the 2nd Amendment, I do not know what does