With something like 280 million guns already floating around out there in the country, laws to make it a little harder to buy a new one wouldn't be as effective as something else that might --- ammunition control.
Without ammo, a gun is just a paperweight.
And unlike guns, ammo has a short shelf life, as Marc Ambinder points out in "Guns Need Food. Starve Them"
Ammunition degrades because the gunpower inside of it does not last forever in the compressed state that it lives. The accuracy of a bullet declines slowly over time. Heat is especially bad for ammunition of all types. The more times you chamber a round, the likelier it will degrade. For most people, the decline in accuracy is mitigated somewhat by the fact that they never use their firearms for self-defense purposes. But it really can be a problem in the long-run. And that's why ammo manufacturers are even more profitable than gun manufacturers.Exempt ammo that is used strictly for hunting and sport shooting.
Let's put aside the cartridges used for hunting and sporting. Those are easily identifiable. We can exclude them from this exercise.Then ban online ammo sales sites like this one.
Require that anyone who purchases such ammo must undergo the same criteria as is required to buy a gun. That makes it more difficult for someone who is not legally allowed to buy a gun to steal one or pick one up at a gun show and then go buy ammo for it.
And let's ban high-capacity clips.
I would add a tax on ammunition sufficient to discourage anyone from hoarding large stockpiles.