Undetectable Firearms Modernization Act

H.R. 4221, the Undetectable Firearms Modernization Act, proposes to update the prohibition on undetectable firearms codified at 18 U.S.C. § 922(p). The bill replaces several old references with new definitions and detection standards that align with more modern security screening equipment (including devices used at airports) and adds precision around what parts of a firearm are considered “major components” and what constitutes detectable material. It also clarifies that prototype firearms are included in the assessment and creates specific exemptions for firearms possessed by the United States or manufactured/imported under existing U.S. government contracts. Overall, the bill seeks to redefine how detectability is measured and which firearms are subject to the undetectable-firearm prohibition.