H.R. 4221: Undetectable Firearms Modernization Act
Sponsor
Madeleine Dean
Democrat · PA-4
Bill Progress
Latest Action · Jun 27, 2025
Referred to the House Committee on the Judiciary.
Keeping undetectable guns out of airports and courthouses
Why it matters
The law meant to keep guns from slipping past airport security was written in 1988 — and it still measures detection against the X-ray machines and metal detectors of that era. H.R. 4221 rewrites that test for today's scanners and today's firearms, including guns built largely from plastic or other low-metal materials, and closes it around prototypes that the old language left ambiguous. Nothing in the bill adds new funding or penalties; it sharpens the definitions that decide what counts as a legal, detectable gun.
H.R. 4221, the Undetectable Firearms Modernization Act, doesn't spend money or create a new program. It rewrites the existing federal ban on guns that can evade security screening.
The old rule said a firearm had to be as detectable as a "Security Exemplar" — a reference piece of stainless steel — when scanned by metal detectors calibrated to find it. The bill drops that calibration language and instead requires a firearm to contain "detectable material" once everything but its major components is removed.
It defines detectable material precisely: material that gives off a magnetic field as strong as 3.7 ounces of a specific grade of stainless steel. It also broadens the airport test, swapping the reference to "x-ray machines" for "detection devices commonly used at airports for security screening" — so the standard isn't locked to one obsolete technology.
Two other changes tighten the edges. The ban is spelled out to cover any firearm, including a prototype, and an older exception for firearms tested by the Treasury is struck. Exemptions for guns under U.S. government control, and for licensed makers working under an existing government contract, stay in place.
H.R. 4221 Bill Summary
What H.R. 4221 actually does.
Replaces the 1988 calibration test with a clear material standard
Instead of requiring a gun to be as detectable as a reference 'Security Exemplar' under specially calibrated detectors, the bill requires the firearm to contain detectable material once all parts except major components are removed.
Sets a 3.7-ounce detectability benchmark
The bill defines 'detectable material' as material that produces a magnetic field as strong as the field from 3.7 ounces of 17-4 PH stainless steel, giving the law a single measurable standard.
Updates the airport test beyond X-ray machines
The old text referred only to 'x-ray machines commonly used at airports.' The bill broadens it to 'detection devices commonly used at airports for security screening,' so the rule isn't tied to one technology.
Spells out which parts count as major components
A 'major component' is defined as the slide or cylinder, or the frame or receiver — and for a rifle or shotgun, the barrel as well — clarifying which parts must register on screening.
Covers any firearm, including a prototype
The bill adds 'including a prototype' to the prohibition, making clear that experimental and not-yet-commercial designs are covered.
Strikes the old Treasury testing exception
The bill removes a sentence that had carved out firearms tested by the Secretary of the Treasury, eliminating that older exception.
Keeps the government and contractor exemptions
Firearms under the control of the United States stay exempt, as do guns handled by a licensed manufacturer or importer under an existing contract with the U.S. government.
Who benefits from H.R. 4221?
People moving through screened spaces
Travelers, courthouse visitors, and stadium crowds rely on metal detectors and scanners catching weapons. The bill aims to keep that screening effective against guns designed with little detectable metal.
Security and screening personnel
TSA officers and other screeners would work under a standard tied to the detection devices they actually use, rather than to 'x-ray machines' named in 1988.
Law enforcement and prosecutors
Sharper definitions of 'major component' and 'detectable material,' plus the explicit inclusion of prototypes, give them clearer lines to enforce and charge against.
Who is affected by H.R. 4221?
Makers of low-metal or plastic firearms
Designers whose guns rely on plastic or other low-metal materials would have to ensure the firearm still contains detectable material once stripped to its major components.
Prototype and experimental gun builders
By adding 'including a prototype,' the bill removes any argument that test or pre-production models fall outside the ban.
Licensed manufacturers and importers
They would need to meet the revised standard, unless they are acting under an existing contract with the U.S. government, which remains exempt.
HR4221 Legislative Journey
House: Committee Action
Jun 27, 2025
Referred to the House Committee on the Judiciary.
About the Sponsor
Madeleine Dean
Democrat, Pennsylvania's 4th congressional district · 7 years in Congress
Committees: Foreign Affairs, Appropriations
View full profile →
Committee Sponsors
Judiciary Committee
0 of 42 committee members cosponsored
No committee members have cosponsored this bill
18 Democrats across this committee haven't cosponsored yet. Mobilize their constituents
H.R. 4221 Quick Facts
- Committee
- Judiciary
- Chamber
- House
- Policy
- Crime and Law Enforcement
- Introduced
- Jun 27, 2025
Referred to the House Committee on the Judiciary.
Jun 27, 2025
Official Sources
Official bill page with status, text, sponsors, and actions for the Undetectable Firearms Modernization Act.
The bill directly amends 18 U.S.C. 922(p), so the U.S. Code text is the core legal reference.
Official House-maintained U.S. Code page for the firearms chapter containing section 922.
The bill refers to detection devices commonly used at airports for security screening, which TSA administers.
Official TSA guidance on firearms in airport screening context helps explain the bill's focus on screened transportation settings.
ATF is the federal agency most closely associated with firearms regulation and enforcement relevant to section 922.
The bill preserves exemptions for licensed manufacturers and licensed importers under U.S. contracts.
PDF version of the official U.S. Code section containing the undetectable firearms provision the bill updates.
H.R. 4221 Common Questions
How much metal does a gun need to be detectable under H.R. 4221?
It has to contain material that gives off a magnetic field as strong as 3.7 ounces of 17-4 PH stainless steel, measured after everything but the major components is removed. That single benchmark replaces the old calibration test.
What does H.R. 4221 change from the 1988 undetectable firearms law?
Two big things. It drops the old 'Security Exemplar' calibration test for a clear 'detectable material' standard, and it broadens the airport test from 'x-ray machines' to the detection devices commonly used for security screening today.
Does H.R. 4221 ban 3D-printed or plastic guns?
It doesn't single them out by name. The bill applies to any firearm that lacks detectable material once stripped to its major components — so a gun built mostly from plastic or other low-metal materials could fall under the ban.
Can prototype guns be banned under H.R. 4221?
Yes. The bill adds the words 'including a prototype' to the prohibition, so experimental and not-yet-commercial designs are explicitly covered, not just finished products.
What gun parts count as major components under H.R. 4221?
The slide or cylinder, and the frame or receiver. For a rifle or shotgun, the barrel counts too. Those are the parts that must still register on screening once everything else is removed.
Can a gun be illegal if airport scanners can't show its shape?
Yes. The bill prohibits a firearm if the detection devices commonly used at airports for security screening would not produce an image that accurately shows the shape of a major component.
Can the government still possess these firearms under H.R. 4221?
Yes. Firearms under U.S. government control stay exempt, and licensed manufacturers or importers can still make, import, or deliver them under an existing contract with the United States.
Does H.R. 4221 add new penalties or funding?
No. The bill rewrites the definitions inside the existing federal ban — it doesn't create a new fine, set a penalty amount, or authorize any spending. Enforcement runs through the firearms laws already on the books.
Based on H.R. 4221 bill text
H.R. 4221 Bill Text
“To modernize the Undetectable Firearms Act of 1988.”
Source: U.S. Government Publishing Office
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