+1 Hornady and Drew.
IIRC, anyone between 17-42 is in the unorganized militia (USC chap 10, sect 311, right?), and Miller v US did say that the 2nd referred to military pattern weapons (which is why the guy's sawed off, being a non-mil weapon, wasn't protected from NFA regulation). By all rules and regs, I can't see any constitutional reason why I shouldn't be able to purchase the exact same weapons that the military has, assuming I can find a buyer.
I don't apply that to chemical/biological/nuclear weapons, though, as I don't think anyone, most especially the government, is responsible enough to have them. No one should be able to purchase nukes.**
**I'm not an idiot, though, and I'm not lobbying for the govt to give up all nukes etc. I just thought I'd add my "nuke exclusion clause" as a defense against the anti's response of "well if you think citizens should be able to buy machineguns, why not nuclear warheads?" The world isn't so ideal, though, and because we live with other countries that DO have nukes, of course our country should have em.