This bill rewrites key parts of 18 U.S.C. § 922(p) to move the law from an outdated, device-focused test toward an objective, material-based standard. It eliminates the Security Exemplar benchmark and instead treats a firearm as undetectable if any non-major part contains no ‘‘detectable material,’’ defined by a magnetic-field equivalence to a specified amount of stainless steel.
The bill also clarifies which pieces count as ‘‘major components,’’ explicitly covers prototypes, and narrows statutory exemptions to firearms in federal possession or those made under existing federal contracts by licensed manufacturers or importers.
For practitioners, the change converts an arguably subjective enforcement regime into one that hinges on measurable material properties — a shift that affects hobbyists and small producers who rely on polymer components, commercial manufacturers that use mixed materials, and federal agencies responsible for screening and enforcement. The new definitions and narrowed exemptions create clearer targets but also raise practical testing and compliance questions that agencies and courts will have to resolve.
At a Glance
What It Does
Replaces the Security Exemplar and device-descriptor language in 18 U.S.C. § 922(p) with a material-based prohibition: a firearm is covered if any non-major part ‘‘does not contain detectable material.’’ It defines ‘‘major component’’ to include slide/cylinder and frame/receiver, and adds the barrel for rifles and shotguns. The bill explicitly brings prototypes within the statute and limits exemptions to federal possession and licensed manufacturers or importers performing under existing U.S. contracts.
Who It Affects
3D-printing hobbyists, small makers, and sellers of polymer-only firearm parts; commercial manufacturers who use nonmetal components; federal enforcement and screening agencies (e.g., ATF, TSA) that must apply the new material standard; and licensed manufacturers working under federal contracts who retain a narrow exemption.
Why It Matters
The Act replaces an ambiguous detector-based test with an ostensibly objective magnetic-field threshold, which should reduce gap arguments based on screening equipment variety but will require new testing protocols. The change targets the growth of polymer and 3D-printed 'ghost gun' components while creating compliance tasks for industry and enforcement.
More articles like this one.
A weekly email with all the latest developments on this topic.
What This Bill Actually Does
At present, the Undetectable Firearms Act prohibited weapons that could defeat particular detection equipment by referencing a ‘‘Security Exemplar’’ and device-specific descriptions (walk-through metal detectors and certain x-ray machines). This bill drops that equipment-specific framing and instead makes detectability turn on the materials used in the firearm’s non-major parts.
Under the new language, if any part other than a defined major component lacks the specified ‘‘detectable material,’’ the firearm falls within the statute.
The measure also tightens the statute’s definitions. It lists which elements count as a firearm’s major components—slides or cylinders and frames or receivers—and adds barrels for rifles and shotguns.
That narrows the scope of the parts that can lawfully be made entirely from non-detectable materials; major components can still contain less-detectable materials without triggering the prohibition under the bill’s structure.Two other practical changes matter. First, the bill explicitly says prototypes are included, closing a potential loophole for experimental builds.
Second, it reworks exemptions: the safe harbor no longer reads as a broad carve-out but instead applies only where the firearm is in federal possession or when a licensed manufacturer or importer makes or transfers a firearm under an existing federal contract. That approach preserves government access while removing a broader commercial exemption that some have used to argue immunity for certain nonmetal production.Implementation depends on how ‘‘detectable material’’ is measured in practice.
The bill defines that concept by reference to a magnetic-field equivalence (the strength produced by a precise amount of a particular stainless steel), which is a technical standard but not an explicit testing protocol. Enforcement will therefore require agencies to adopt or reference measurement methods and thresholds, and regulated parties will need clarity about testing labs, measurement units, and tolerances if manufacturers are to design compliant parts.
The Five Things You Need to Know
The bill defines ‘‘detectable material’’ as material producing a magnetic field equivalent in strength to 3.7 ounces of 17‑4 PH stainless steel.
It defines ‘‘major component’’ to mean the slide or cylinder, the frame or receiver, and—specifically for rifles and shotguns—the barrel.
The statutory prohibition explicitly applies to prototypes; the bill inserts the word ‘‘including a prototype’’ into the covered conduct.
Language referencing ‘‘walk-through metal detectors calibrated to detect the Security Exemplar’’ and specific x‑ray formulations is replaced with references to ‘‘detection devices commonly used at airports for security screening.’, The exemption is narrowed so it only applies to firearms in U.S. government possession or firearms manufactured, imported, or transferred by licensed manufacturers/importers pursuant to an existing contract with the United States.
Section-by-Section Breakdown
Every bill we cover gets an analysis of its key sections.
Short title
Sets the Act’s short title as the ‘‘Undetectable Firearms Modernization Act.’
Replaces equipment-based detectability language with a materials test
Strikes the old phrasing that compared parts to a ‘‘Security Exemplar’’ detectability benchmark and replaces it with a rule that treats parts other than major components as covered if they ‘‘do not contain detectable material.’’ Practically, this moves the inquiry away from how a particular detector reads an object toward whether parts contain a minimum amount of magnetic material.
Broadens screen-type reference to current airport detection devices
Changes references to specific x‑ray machines to a more general standard: a part is undetectable if it ‘‘would not generate’’ the signature expected by detection devices commonly used at airports for security screening. This removes legacy machine names and signals an intent to cover contemporary screening technologies, though it does not prescribe how to map material properties to those device outputs.
Clarifies what counts as a major component and sets a magnetic-field threshold
Adds a statutory list of ‘‘major components’’ (slide or cylinder; frame or receiver; and barrel for rifles/shotguns) and supplies a quantitative definition of ‘‘detectable material’’ by pegging it to the magnetic field strength of 3.7 ounces of 17‑4 PH stainless steel. That numeric anchor is unusually specific for criminal statutes and will drive how labs, manufacturers, and courts measure compliance.
Includes prototypes in the prohibition
Inserts ‘‘including a prototype’’ into the description of covered firearms. The legislative drafter removed the second sentence of paragraph (3), streamlining the subsection and making clear that experimental builds are treated equivalently to produced firearms under the law.
Narrows exemptions to federal possession and existing U.S. contracts
Replaces broader language with a two-part exemption that applies only where a firearm is in U.S. possession or where a licensed manufacturer/importer acts under an existing contract with the U.S. That change preserves federal procurement while removing a previously broader carve-out that some argued allowed commercial nonmetal production to escape the statute.
This bill is one of many.
Codify tracks hundreds of bills on Criminal Justice across all five countries.
Explore Criminal Justice in Codify Search →Who Benefits and Who Bears the Cost
Every bill creates winners and losers. Here's who stands to gain and who bears the cost.
Who Benefits
- Federal security and screening agencies — The objective, material-based standard gives agencies a clearer statutory yardstick to claim compliance and enforcement authority against polymer-only weapons and may simplify coordination with testing labs.
- Law enforcement — Police and prosecutors gain a more definite statutory definition to use in cases involving 3D-printed or polymer-framed firearms, reducing reliance on device-specific expert testimony about particular detectors.
- Licensed manufacturers with federal contracts — Those already under existing U.S. contracts retain a narrow exemption, preserving ongoing government supply lines and avoiding immediate disruption for contract fulfillment.
Who Bears the Cost
- Hobbyists and small-scale 3D-printing producers — Individuals and micro-enterprises that make or sell polymer parts risk criminal exposure because the bill treats prototypes and nonmetal parts without detectable material as covered.
- Commercial designers using mixed materials — Manufacturers who use nonmetal components for weight reduction or performance will face new compliance decisions, potential redesign costs, and testing expenses to demonstrate products meet the magnetic-field threshold.
- ATF and other enforcement agencies — Agencies will need to develop measurement protocols, accredit testing labs, and absorb investigatory and potential litigation costs arising from disputes over measurement methods and the new technical standard.
- Shipping intermediaries and marketplaces — Carriers, online platforms, and secondary-market vendors may confront increased legal risk and takedown or interdiction obligations as the line between legal parts and unlawful parts is redefined.
Key Issues
The Core Tension
The bill pits two legitimate goals against each other: the desire to close a technological loophole that enabled polymer and 3D‑printed firearms from evading metal-based screening, versus the need for a practicable, testable enforcement standard that does not criminalize legitimate research, complicate procurement, or invite endless technical litigation. Solving one side—by setting an objective materials threshold—creates practical and administrative burdens that must be resolved outside the statute.
The bill’s shift to a magnetic-field equivalence is precise in wording but leaves critical implementation questions open. It identifies 3.7 ounces of 17‑4 PH stainless steel as the comparator but does not prescribe measurement methods, sensor types, sample geometry, measurement tolerances, or accredited testing standards.
Magnetic response depends on part geometry, thickness, and alloy composition; identical masses of different shapes or alloys can produce different detector responses. That technical gap means disputes over compliance will likely migrate into laboratories and expert testimony unless agencies or standards bodies provideProtocols and calibration methods.
The statutory inclusion of prototypes and the narrowing of exemptions create enforcement clarity but also risk chilling research and legitimate experimentation. Universities, defense contractors developing prototype weapons for testing, and small innovators could find themselves operating in legal uncertainty unless ATF issues guidance or carve-outs.
Similarly, the exemption limited to firearms ‘‘received by, in the possession of, or under the control of the United States’’ plus licensed manufacturers/importers acting ‘‘pursuant to an existing contract with the United States’’ raises questions about ongoing contract changes, subcontracts, state and local government testing programs, and whether transitional production for future contracts is covered.
Finally, replacing equipment-specific language with a material standard improves durability against changing detection tech but severs the direct link between legal prohibitedness and how screening equipment actually behaves. That trade-off simplifies statutory text but may complicate operational screening decisions at airports and ports, since detection devices measure electromagnetic and imaging signatures that depend on more than simple magnetic-field strength.
Try it yourself.
Ask a question in plain English, or pick a topic below. Results in seconds.