Since Roe v. Wade, Conservatives in many states have effectively gone around the laws prohibiting restrictions on abortion by making it next to impossible to operate an abortion clinic or to provide abortions. So I say two can play at that game.
If we cannot place restrictions on whether people can own guns, how about this? People can own as many guns as they want... they can own the most dangerous kinds of guns the gun makers can create. However, ammunition is now severely restricted. Each person is only allowed six bullets. If they use them up, they need to bring the spent casings to the store in order to get another six. And no, you can't just go to another store and buy another set. When you buy ammunition, your name is placed into a central database that the stores have to check first before they can sell it to you. This is already in place when you buy restricted allergy medication in a pharmacy. You can't just go to another pharmacy to buy more. It shouldn't be too hard to implement this for ammunition sales.
Anyone who sells ammo will need to be licensed, just like one needs a license to sell liquor. Breaking the laws on ammo sales will cause your license to be revoked, as well as possible jail time.
Possession of a quantity of ammunition exceeding a certain amount will be a felony, and can get you the same number of years in the slammer as possessing a certain amount of marijuana. Also, carrying ammo across state lines will also be illegal.
Sure, drug dealers and cartels will probably go around this restriction, but then again, they don't normally walk into schools firing into crowds of children.
And if, God forbid, some kid goes on another shooting rampage, whoever supplied him (and it's usually a him) that ammunition will be liable. Parents will no longer be off the hook for the actions of their kids (if the kid got the guns from his parents).
No, I'm not a lawyer and the 2nd Amendment probably applies to ammunition as well as the guns... Does it? Anyway, I did say it was a crazy proposal.