There is not a word in the Miller opinion to support the "collective" right notion. What there is, which is arguably reading limitations into the Second Amendment that aren't there, is a holding that guns only qualify as a Second Amendment-protected right if they are a type which can have a military use. As you probably know, the court in Miller did NOT hold that the defendants didn't have a right to own the sawed-off shotguns in question -- the court remanded the case to the lower court for a determination of fact on whether sawed-off shotguns had any legitimate military use. The historical facts show clearly that they do, but the lower court never addressed the remanded case, as one defendant had died and the other had agreed to pay a fine and be done with the whole thing.
Any legitimate reading of the Miller decision concludes that while it did not confirm our individual right to own "Saturday Night Specials", it most certainly DID confirm our individual right to own any and all guns that have potential military applications, which obviously includes full-auto machine guns, 50 calibers, guns with large capacity magazines, bayonet mounts, flash suppressors, pistol grips, folding stocks, and grenade launchers.
Shotguns, yes. Less than 18", no.