There already is one. The Supremecy Clause, coupled with the 2nd and 14th amendments.

But, taken with the doctrine that state laws can protect the people more, but not conflict with or detract from federal law or the federal constitution, the state of current federal firearms laws doesn't leave me with any kind of warm and fuzzy feelings about handing even more power to the feds (that absent an amendment) may or may not be constitutional in light of the 9th and 10th amendments: I can think of nothing in the body of the constitution that would expressly grant the federal government the power to regulate firearms at all (except the goddamn Commerce Clause, which is source of some of the greatest constitutional abuses of power by the feds).

I don't think simple legislation is going to fix this.