New Federal Law Defines 'Undetectable Firearms' with Specific Magnetic Field Standard

This legislation, titled the Undetectable Firearms Modernization Act, is a technical update to federal law (Title 18, Section 922(p)) that governs firearms that are hard to detect by security equipment. Think of those mostly plastic guns that have been a concern for airport security and secure facilities. The bill’s main purpose is to drag the definition of an “undetectable firearm” out of the 1980s and into the age of 3D printing and modern security scanners.

The Security Standard Gets a Precision Tune-Up

The biggest change is how the government decides if a gun is too hard to find. Previously, the rules were a bit squishy, relying on whether certain parts (like grips) were less detectable than a specific reference model. This bill changes the test to focus on the whole firearm: all parts of the gun, except for the major components, must now contain detectable material when run through a metal detector calibrated to a specific “Security Exemplar.”

They are also getting hyper-specific about what “detectable” actually means. The new law defines “Detectable Material” as anything that creates a magnetic field equal in strength to the magnetic field produced by 3.7 ounces of 174 PH stainless steel. This is a huge shift, replacing vague language with a concrete, measurable standard. For manufacturers, this clarity is crucial; they now have a precise metric to meet, rather than a subjective metal detector test. For the rest of us, it means the rules are less about guesswork and more about physics.

What Counts as a Gun, and Who Gets a Pass?

The bill also tightens up what parts of a gun must be detectable and who is exempt from the ban. The law now clearly defines “Major Components”—for a handgun, that’s the slide/cylinder or the frame/receiver; for a rifle or shotgun, it also includes the barrel. These are the parts that must meet the new detectability standards.

In a move to close potential loopholes, the prohibition is explicitly extended to include any “prototype” of an undetectable firearm. If you’re tinkering with a plastic gun design in your garage, the new rules apply to your test model, too. However, there are clear exemptions for government operations: the ban won’t apply to firearms already possessed by the U.S. government, or those manufactured under an existing contract for the U.S. government. This ensures that federal agencies can still use specialized equipment without violating the new rules.

Real-World Impact: Better Security, Higher Bar for Manufacturers

For the average person going through an airport or courthouse, this modernization should mean better security. By updating the technical standards, the law aims to ensure that modern security scanners are actually capable of catching modern, non-traditional firearms. The old rules simply didn't keep pace with technology, allowing for potential gaps in security.

For licensed manufacturers, this means they must ensure their non-major components contain enough of that specific magnetic material to hit the 3.7-ounce stainless steel equivalent mark. This might require some retooling or material changes, especially for companies that rely on lighter or non-traditional materials. The benefit is a clear target to aim for, but the cost is the necessary compliance update. Ultimately, this bill is less about changing who can own guns and more about ensuring that if a gun is present in a secure area, the security equipment designed to find it actually works.