The Undetectable Firearms Act: Issues for Congress
INSIGHTi
The Undetectable Firearms Act: Issues for
Congress
March 4, 2024
In the 1980s, the production of guns made with polymer (industrial plastic) stoked concerns that firearms
were becoming undetectable by metal detectors in places like airports and federal buildings. In response,
Congress passed, and President Ronald W. Reagan signed into law, the Undetectable Firearms Act of
1988 (UFA; P.L. 100-649).
The UFA was codified as 18 U.S.C. §922(p) and prohibits owning, purchasing, importing, receiving, and
selling firearms that do not include at least 3.7 ounces of stainless steel. The UFA also prohibits handguns
where the barrel, slide or cylinder, or the frame or receiver do not generate an image that accurately
depicts the shape of the component when under inspection by the type of x-ray machine commonly used
at airports.
The UFA included a sunset clause, after which its provisions will be repealed. The UFA’s sunset has been
delayed multiple times, most recently through March 22, 2024 (P.L. 118-40).
History of Undetectable Firearms Act
The impetus for the UFA stemmed from fears that polymer-framed firearms could slip past airport metal
detectors. For example, the Glock was invented in the 1980s and is a polymer-framed, semi-automatic
pistol. Initially designed for the Austrian military, the Glock’s frame weighs much less than traditional
steel-framed firearms and the polymer allows it to better absorb recoil than other handguns.
Some observers framed the Glock as a hijacker’s special, referring to the potentiality that it could pass
through airport security undetected. Additionally, in 1986 media reports claimed that the Glock, when
dismantled, “is frighteningly easy to smuggle past airport security” and that “one Pentagon security expert
decided to demonstrate just how easy it would be to sneak a Glock 17 aboard an airliner.” Though not
mentioned in these articles, these same metal detectors and their operators were also often not recognizing
pistols made exclusively out of metal.
Beyond concerns over polymer guns, some feared that individuals may attempt to board aircrafts or enter
federal buildings with nondescript, gadget firearms or firearms that, when broken into component parts,
do not look like traditional firearms—such as “a James Bond-like pen gun.”
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18 U.S.C. §922(p), as enacted by the UFA, prohibits the manufacture, importation, transfer, or possession
of any firearm that is not detectable to walk-through metal detectors calibrated to detect a gun with the
same electromagnetic signature as 3.7 ounces of stainless steel. Moreover, any gun and its component
parts (barrels, slides, cylinders, frames, or receivers), when in an x-ray machine, are required to look like
those on a traditional gun and not be disguised as another object. Notably, the stainless-steel provision
does not require that the steel be from an operable part of the firearm and can be overcome by attaching a
removable steel block to the frame or receiver. At the time of enactment, the UFA did not ban any mass-
produced firearm, including the Glock.
Issues for Consideration
Unless the sunset is once again delayed, or alternatively made permanent, the UFA will be repealed on
March 23, 2024. Among the potential concerns about the UFA’s pending repeal are three that may be of
interest to policymakers:
The volume of undetectable firearms that may be flowing through prohibited areas. According to
data from the Transportation Security Administration (TSA), the number of firearms detected at airport
security checkpoints increased to an all-time high of 6,737 in 2023. If the UFA is repealed, individuals
who may attempt to pass through airport security with firearms might seek out those that are undetectable
by airport security.
3D-printing of firearms. While 3D-printing of firearms involves significant start-up costs and
uncertainty about their effectiveness, an individual could use a 3D-printer to produce a polymer firearm
that may not be recognized by a metal detector at an airport or other building. If the UFA is repealed,
absent other changes to firearms regulations, 3D-printed firearms that may be undetectable by existing
security screening methods would become legal to produce, purchase, and transfer, and could pose a
greater risk to public safety in places where firearms are prohibited.
Decriminalization of non-traditional-looking handguns. If the UFA is repealed, absent other changes,
handguns with component parts that do not look like those in traditional handguns and instead appear as
nondescript objects when subjected to an x-ray machine like those in airports would be decriminalized.
These types of weapons are, by design, difficult to detect and may present security challenges in a variety
of settings.
Policy options available to Congress with regard to the UFA’s pending repeal include letting the UFA be
repealed as scheduled under current law, delaying its repeal by a specified amount of time, making the
UFA permanent, amending the UFA, or enacting a different provision to accomplish similar ends. In
addition to the UFA’s pending repeal, Congress may consider questions about the utility of the UFA.
While there are individual instances of undetectable weapons being found, according to an Urban Institute
study commissioned by the Bureau of Justice Statistics (BJS), between 2000-2016 there were no criminal
cases filed in U.S. district courts where 18 U.S.C. §922(p) was one of the five leading charges.
Nonetheless, there is a relevant penalty in 18 U.S.C. §924(f) which states that knowingly violating 18
U.S.C. §922(p) is punishable by up to five years in federal prison and a fine. According to data collected
by BJS, between 2000-2022 there were 146 persons convicted under 18 U.S.C. §924(f). This suggests that
while possessing an undetectable firearm is rarely if ever a lead charge in criminal filings, it has been
charged and convictions have been obtained for related offenses in federal court.
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Author Information
Jordan B. Cohen
Analyst in Firearms Policy
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