According to CBS News:
“A federal law that makes it harder to sneak firearms past metal detectors is set to expire in just a few weeks. A local congressman is pushing for bipartisan support to keep the law on the books. Seventeen quarters, two dimes and a nickel is metal weighing 3.7 ounces, and that’s the minimum amount of metal federal law requires in all firearms so they cannot be sneaked past metal detectors, such as those used at music and sporting events. “Because it’s common sense. It’s about insuring the safety of the public and preventing criminals from using undetectable firearms,” said Rep. Mike Lawler, a Republican representing parts of the Hudson Valley …”
The law is largely unenforceable crap and, in light of the Bruen decision, might not stand up in court.