The rationale that machine guns are not protected (and therefore illegal) because they're "unusual" even though they're only unusual because they're illegal, is astounding to me.
And to me, also. There is an excellent thread over on THR about muskets and assault weapons, and one of my posts there seems particularly apt for this discussion.
The "Assault Weapon" of the late 18th Century was the Brown Bess (or Charleville) Musket. It has most of the characteristics of the modern assault rifle -- fast-firing (compared to a patched ball in a rifle) accurate only at short to intermediate range, not well suited to hunting (although usable as such), fast to reload, designed to mow down humans as quickly as possible given the technological limits of the age. Moreover the smoothbore musket was often used with multiple projectiles (Buck and Ball Loads) to increase its effectiveness.
It is exactly the type of weapon our forefathers intended for us to "keep and bear" so that we, as a militia, would have parity with an invading army or an army raised by our own tyrannical government.
The Brown Bess to M-16 is less of a technological change than the printing press to the TV broadcast, yet those who would scream like wounded panthers at the thought of government censorship of radio and TV broadcasts would deny us the right to own true (select-fire) assault rifles under the theory that they weren't available at the time the 2nd Amendment was written.
We may well be stuck with the requirement for licensure for concealed carry (albeit shall-issue) due to early 19th Century views about concealed weapons as evil, but oft-quoted militia clause of the 2nd Amendment makes it clear that "assault weapons" are the class of weapons most protected by the core of the 2nd Amendment.