[Evan Thomas]

Good points, BR.

Yes, focusing on what counts as "unusual" seems a more promising way to go. As I wrote in Part I of this discussion, "...pump shotguns must be about as 'unusual' as F150's..."

As Glenn pointed out above, "dangerous" is very much in the eye of the beholder -- but "unusual" could be defined in some objective, i.e. quantitative, way, at least in principle. (Care would be needed in the definition, however, lest it effectively prohibit innovations in design.)

While it's possible to argue, qua Yellowfin, that the standard of "in common use at the time" may be "unfairly" influenced by previous restrictions, as in those on FA weapons, I'm not sure this is a useful tactic. I agree with those who've suggested that FA is a "bright line" (where did that expression come from, anyway?) that's not worth pushing at for any number of reasons, including both actual and perceived dangerousness.