I have some reservations about pinning hopes on the "common use" concept. It would not be beyond the pale for the Feds to ban a sweeping category of weapons(1986 Machine Gun Ban), fight the law through the system for God-knows how many years and then claim it's constitutional because the firearms in question are not in common use, yet the only reason they're not in common use is because they're banned.
What's to stop them setting up an updated NFA system that charges $3,500 instead of $200 and adding different firearms and components to it over time until they're no longer in common use and then banning them entirely?
Vertical foregrip? NFA item.
15 round (or larger) magazines? NFA item.
Slow and steady, loses the rights.
Still happily answering to the call-sign Peetza.
You do not HAVE a soul. You ARE a soul. You HAVE a body.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.