The Second Amendment is in the Constitution as the second of our NATION’S Bill of Rights. Therefore, it’s long past time for Federal Preemption of all state laws regarding firearms. In similar fashion to how States presently “enjoin” local entities from passing gun laws, so now should the Federal Government preempt the States. And yeah I know that people who currently live in “relatively free states” as regards gun control will come out here and pi$$ and moan that such a move would “take away their sovereignty,” but even in their states, they cannot guarantee that a RAT invasion in the not too distant future could remove their Second Amendment “freedoms” with the stroke of a pen. And along with Federal Preemption, should come an iron-clad ruling from the SCOTUS that the new law “is Constitutional and the Law of the Land” as settled law.
The way I see it, is that the Constitution and Bill of Rights are also a contract with the states, in that they cannot arbitrarily deny people their Natural Rights.
The incorporation clause of the 14th Amendment will also undoubtedly support and allow the law that you proposed.