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The ghost gun industry has skirted the law and fueled violence by creating a dangerous market in gun build kits and other products that allow people to arm themselves and assemble untraceable weapons without background checks or other protections. 

In recent years, many communities have experienced an explosion in the unregulated, untracked sale of “DIY” ghost gun kits and related products that have allowed people to easily assemble their own untraceable guns without any background check, serial number, sale record, or other protections. In 2022, the Biden Administration took vital executive action to begin address this ghost gun crisis at the federal level but executive action can only do so much; a more comprehensive legislative response is still needed from Congress and statehouses to reform the ghost gun industry. In recent years, a number of states have enacted critical reforms to stop the unchecked proliferation of these unserialized guns.


In the last decade, there has been an exploding market in “DIY” ghost guns that seek to intentionally circumvent the reach of state and federal gun safety laws. The ghost gun industry has developed gun build kits and related products that allow untrained amateurs to quickly and easily assemble their own firearms from unregulated parts—including frames and receivers that are left just unfinished enough to escape the definition of “firearm” under state or federal gun safety laws.

The weapons assembled from these kits and related products are called “ghost guns” because they are typically sold and assembled without traceable serial numbers. Many are also sold anonymously without any background check or sale record by unlicensed manufacturers and sellers evading laws governing licensed gun manufacturers and dealers. Furthermore, ghost guns may be produced largely or even entirely from plastic, which can render them undetectable by traditional metal detectors and other security scanning systems. Ghost gun purveyors thus provide access to untraceable, undetectable firearms to individuals who have not passed—and potentially could not pass—a background check.

The essential component of many ghost gun build kits is an “unfinished” frame or receiver. The ghost gun industry typically leaves these products just unfinished enough to argue that they should escape the definition of “firearm” used in relevant gun safety laws. (The industry often markets unfinished receivers as “80% receivers” under the claim that they are 80% finished.) The frame or receiver is such an integral part of the weapon’s design and function that federal law (and most state laws) define the term “firearm” to include the frame or receiver of the weapon alone without any other parts or components, as well as any weapon or combination of parts that may be “readily converted” to shoot.1 If the frame or receiver of a firearm is completed or can be “readily converted” to shoot, it is considered a “firearm” under federal law and many state laws too, meaning it must generally, among other things, have a serial number imprinted on it prior to sale to a consumer, and that retail sellers of the product generally have to be licensed as firearm dealers, conduct background checks, and retain sale records.

Like completed frames and receivers, the sole function of unfinished frames and receivers is to be used to assemble a weapon designed and capable of ending human life. The primary purpose of selling the frame or receiver in “unfinished” form is to circumvent key federal and state gun safety laws both for the industry that manufactures and sells these products and the buyers who purchase them.

This ghost gun market has been an obviously and dangerously attractive source of weaponry for people who know they would fail a background check to purchase a firearm, including underage minors. A May 2021 report by The Guardian shared this telling anecdote:

When Brian Muhammad, a program manager at a gun violence prevention group in California, asked a 16-year-old boy in 2018 how young people were getting guns, he assumed the answer would be Nevada, the neighboring state with looser gun laws.“Who would waste time going to Nevada when you can just get them in the mail and put it together?” the Stockton teen nonchalantly replied.

The ghost gun crisis has also grown worst in places with the strongest gun safety laws, where gun traffickers and others legally disqualified from buying firearms are most motivated to turn to other sources to acquire deadly weapons.

Why Firearm Serial Numbers Matter for Public Safety

In the traditional manufacturing process, the firearm manufacturer or importer will affix a serial number and markings that identify the manufacturer or importer, make, model, and caliber. Using this information, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) can track firearms from the manufacturer or importer through the distribution chain to the first retail purchaser. ATF works extensively with other law enforcement agencies to trace firearms using this technique—in FY 2022 alone, ATF conducted more than 620,000 traces.2

When law enforcement agencies recover firearms that have been used in crimes, the agencies can usually trace the firearms to their first retail purchaser and use that information to investigate and solve the crime. Tracing is a powerful investigative tool, but it is dependent on the ability to identify firearms based on their serial numbers. Because the purveyors of the parts and kits used to make untraceable guns claim that they are not selling firearms, they also assert that these serialization requirements do not apply to them. Without a serial number, law enforcement cannot run a trace search on a firearm, making it difficult, if not impossible, in many cases to determine the chain of custody from the gun itself.

Making Untraceable and Undetectable Guns

Untraceable guns can also be created using new manufacturing technologies such as 3D printing, which allows a person to produce a three-dimensional object such as a firearm much in the way that a traditional printer can produce a printed document. A high-quality, easy-to-use model is available for about $2,500, roughly the cost of a high-end AR-15–style rifle. Entry-level 3D printers are available for under $200.

In 2012, a self-described anarchist began using 3D-printing technology to create firearms. He developed computer code that would allow anyone with a 3D-printing machine to produce firearm components, including lower receivers, and posted that code on the internet. Receivers manufactured with 3D printers are not as durable as traditional metal receivers, but firearms built using them can be just as deadly. An assault rifle assembled using a 3D-printed lower receiver can fire over six hundred rounds—three times the number fired in the Pulse nightclub shooting that left 49 dead and 53 wounded. He also developed code to produce fully functional firearms from scratch. One such firearm is a pistol made almost entirely from plastic capable of firing a .380-caliber bullet. The only component that wasn’t manufactured using the 3D printer was the firing pin, which was simply an ordinary nail that could be purchased at any hardware store.

With that code publicly available, anyone with an internet connection and a 3D printer could produce a fully functional and unserialized firearm without a background check. And because these downloadable guns can be made entirely, or almost entirely, from plastic, they may be undetectable at security checkpoints that use metal detectors.

Other companies have also developed products such as pre-programmed milling machines that will produce a fully functional firearm receiver from unformed material with the press of a button. (These milling machines carve material in a subtractive manufacturing process while 3D printing adds material in an additive manufacturing process; both products seek to enable people to produce completed, unserialized firearm frames or receivers with the press of a button without ever undergoing a background check or other protections).

Untraceable guns are increasingly used by illegal gun trafficking rings across the country. A 2015 bust of a ghost-gun trafficking ring in Long Island revealed ghost guns as the “new frontier of illegal firearms trafficking.”3 In July 2018, the Los Angeles Police Department broke up a brazen gang-trafficking enterprise in Los Angeles.4 Individuals have been caught manufacturing and selling untraceable guns in locations across the country.5 For example, in April 2018 a New Jersey grand jury indicted a man for unlawfully manufacturing and selling untraceable guns after law enforcement seized nearly three dozen weapons from his home, including nearly 20 untraceable guns.6

Ghost guns have also been used in many mass shootings. In 2014 a man who failed a background check and could not legally purchase a gun built an assault rifle from a ghost gun kit, then used it on a rampage at a college campus in Southern California, firing 100 rounds and killing five people.7 In 2017 a California man prosecutors described as a “deranged, paranoid killer” who was prohibited from owning a gun and under prosecution for multiple crimes, was nevertheless able to kill six people and injure 10 with two assault-style rifles he assembled using parts ordered online.8 In 2019 a sixteen-year-old boy used a self-assembled untraceable firearm in a school shooting in Santa Clarita, CA, killing two students and injuring three others.9

Other tragedies have been narrowly averted. In Pennsylvania, a police officer responding to a call outside Philadelphia shot and killed a person who was legally prohibited from accessing guns but had threatened to shoot the officer with a homemade gun made with parts he ordered online.10 The following month, police averted a school shooting outside Philadelphia by a student who had assembled an untraceable gun he had purchased online.11


We’re in this together. To build a safer America—one where children and parents in every neighborhood can learn, play, work, and worship without fear of gun violence—we need you standing beside us in this fight.

Summary of Federal Law

On April 26, 2022, the Biden Administration took executive action to begin to address the ghost gun crisis. The US Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) issued Final Rule 2021R-05F, entitled “Definition of ‘Frame or Receiver’ and Identification of Firearms,” defining the weapon parts kits that can be readily converted into a fully assembled firearm, including to function as a frame or receiver, as “firearms.” 12 Defining weapon parts kits as firearms requires sellers of these kits to have a federal firearms license, to serialize the parts and retain records, and to conduct a background check before every sale of a kit. The rule, which became effective on August 24, 2022:

  • Adds to the definition of “firearm”:13 
The term shall include a weapon parts kit that is designed to or may readily14 be completed, assembled, restored, or otherwise converted to expel a projectile by the action of an explosive. The term shall not include a weapon, including a weapon parts kit, in which the frame or receiver of such weapon is destroyed as described in the definition of “frame or receiver”.

As such, “80%” build kits, which include a partially completed frame or receiver or “receiver blank”15 and other components necessary to make a functioning firearm–barrels, trunnions, springs, pins, slides (in pistols), uppers (in long guns), and sights–is added to the definition of “firearm” under the Gun Control Act of 1968 (GCA). The addition of this kit to the definition requires manufacturers of the kit to be federally licensed and to include serial numbers on the kit’s frame or receiver, and requires those engaged in the business of selling such kits to also be federally licensed and, thus, conduct background checks on prospective purchasers as required by law.16 This rule does not affect the regulation of firearms built at home from scratch, those assembled with a fully manufactured frame or receiver, or the building of a historical replica.

  • Amends the definitions of “frame” and “receiver,”17 to address technological advancements and judicial developments, ensuring firearms using split or multi-part receivers are regulated under the GCA. As described above, the Gun Control Act provides that the definition of “frame or receiver” determines what items are subject to the federal gun laws requiring a background check and serial number. The amended definition includes: (1) the part that houses or provides a structure for the primary energized component of a handgun, (2) the breech blocking or sealing component of a rifle or shotgun, and (3) the internal sound reduction component of a firearm muffler or firearm silencer. The definition also provides, in part, that the term “frame or receiver”:
[S]hall include a partially complete, disassembled, or nonfunctional frame or receiver, including a frame or receiver parts kit, that is designed to or may readily be completed, assembled, restored, or otherwise converted to function as a frame or receiver.…The terms shall not include a forging, casting, printing, extrusion, unmachined body, or similar article that has not yet reached a stage of manufacture where it is clearly identifiable as an unfinished component part of a weapon (e.g., unformed block of metal, liquid polymer, or other raw material). When issuing a classification, the Director may consider any associated templates, jigs, molds, equipment, tools, instructions, guides, or marketing materials that are sold, distributed, or possessed with the item or kit, or otherwise made available by the seller or distributor of the item or kit to the purchaser or recipient of the item or kit.
  • Requires manufacturers and importers to mark the frame or receiver of new firearms with a serial number and other identifying information, including the name of the manufacturer or importer, or their federal firearm license (FFL) number.18
  • Amends the definition of “gunsmith,” clarifying that licensed dealer-gunsmiths, without being licensed as a manufacturer may:19
    • Perform gunsmithing services on existing firearms for their customers, or for another licensee’s customers, because the gunsmith is not creating firearms for sale or distribution.
    • Purchase complete weapons,20 make repairs (e.g., by replacing worn or broken parts), and resell them. 
    • Make repairs for other FFLs who plan to resell the firearms. 
    • Place identification marks on privately made firearms as a service for an FFL, while under the direct supervision of the requesting FFL.  
  • Requires FFLs (including dealers and gunsmiths) that have, or take into inventory, any “private made firearm (PMF)” to serialize the firearms.21 The rule defines “privately made firearm (PMF)” as “a firearm, including a frame or receiver, completed, assembled, or otherwise produced by a person other than a licensed manufacturer, and without a serial number placed by a licensed manufacturer at the time the firearm was produced.” 22 The term includes both 3-D printed firearms or firearms built using a kit.

The rule neither bans privately made firearms (PMFs) nor restricts a person’s ability to make a PMF if the person is eligible to purchase and possess firearms. The rule also does not prevent an unlicensed person from selling a PMF without a background check.23

Some states have taken stronger action by passing comprehensive state level legislation to reform the ghost gun industry and curb the proliferation of other related products like 3D printers and milling machines designed to produce firearms and key firearm components.

Summary of State Law

Thirteen states (California, Colorado, Connecticut, Delaware, Hawaii, Illinois, Maryland, Nevada, New Jersey, New York, Oregon, Rhode Island, and Washington) and the District of Columbia have enacted laws to at least partially reform the ghost gun industry and regulate the sale and manufacture of untraceable, unserialized ghost guns. Many of these state laws, as well as a longstanding law regulating “plastic guns” in Virginia, also regulate the manufacture, sale, and possession of guns that are undetectable by metal detectors and traditional security screening systems. Further restrictions have also been implemented at the local level in some places.24

The strongest of these state ghost gun laws include provisions to:

  • Ensure that the sale, transfer, and manufacture of both completed and unfinished frames and receivers are subject to the same gun safety laws as fully assembled firearms in that state.
  • Define “unfinished frame or receiver” broadly to encompass products that can be readily completed, assembled, or converted to be used as the frame or receiver and any other product that is that is marketed or sold to the public to become or be used as the frame or receiver of a functional firearm once completed, assembled, or converted.
  • Ensure that people who are legally disqualified from accessing firearms, such as people convicted of serious crimes or subject to domestic violence restraining orders, are also disqualified from acquiring or possessing completed and unfinished frames and receivers.
  • Stop the sale, transfer, manufacture, and possession of undetectable firearms by requiring that all operable firearms be detectable by standard screening systems.
  • Ensure that all firearms, including completed or unfinished frames and receivers, are engraved with a serial number prior to sale or delivery to an unlicensed buyer, and limit possession of unserialized firearms.
  • Halt the sale of any unfinished frame or receiver that is not federally regulated as a “firearm” under federal law (thereby ensuring that these products are sold only if they have valid serial number and that the FBI NICS background check system may be accessed to conduct a full background check on individuals buying these products).
  • Limit the number of firearms, including completed or unfinished frames or receivers, that an unlicensed manufacturer may produce per year without obtaining a manufacturer license.
  • Prohibit unlicensed firearm manufacturers from selling or transferring ownership of firearms that they manufacture or cause to be manufactured. (Hobbyists should be able to continue to assemble firearms for personal use only or obtain a firearm manufacturer’s license in order to produce and furnish firearms for others).
  • Prohibit companies from selling 3D printers or computerized milling machines that have the primary function of manufacturing firearms (including completed or unfinished frames and receivers) to unlicensed firearm manufacturers, and prohibit unlicensed firearm manufacturers from using such machines to produce firearms, including completed or unfinished frames and receivers.
  • Restrict the indiscriminate distribution of code to produce guns from 3D printers or computerized milling machines—for example, only allow distribution to a specific individual after a background check has been conducted, or only allow distribution to licensed firearm manufacturers.
  • Make companies or individuals who indiscriminately disseminate that code liable for any harm that occurs as a result.


Gun violence is a complex problem, and while there’s no one-size-fits-all solution, we must act. Our reports bring you the latest cutting-edge research and analysis about strategies to end our country’s gun violence crisis at every level.

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  1. See 18 USC § 921(a)(3).[]
  2. Bureau of Alcohol, Tobacco, Firearms and Explosives, “Fact Sheet- Facts and Figures for Fiscal Year 2022,” January, 2023,[]
  3. Office of the Attorney General of the State of New York, “A.G. Schneiderman Announces Thirty-Two Count Indictment of Two Defendants Charged with Illegally Trafficking Untraceable ‘Ghost Guns,’” news release, September 21, 2015,[]
  4. Richard Winton, L.A. Gangs Stockpile Untraceable ‘Ghost Guns’ that Members Make Themselves, Los Angeles Times, July 6, 2018,[]
  5. E.g., Tamara Sacharczyk, “Unregistered, Untraceable Guns Recovered in Massachusetts,” WWLP News 22, March 28, 2018,; Alex Ceneviva, “Bridgeport Police Confiscate Ghost Guns,” WTNH News 8, August 2, 2018,; Lauren Sellew, “Warrant: Authorities Began Investigating Southington Man Charged with Firearm Offenses When He Tried to Sell Homemade Rifle Online,” Record-Journal, November 21, 2018,[]
  6. Maxwell Reil, “Man indicted after selling ‘ghost gun’ in Hammonton,” Atlantic City Press, April 13, 2018,[]
  7. Robert Cavnar, “Santa Monica Shooter Built His Gun From Parts He Bought Online,” Huffington Post, June 15, 2013,[]
  8. Ray Sanchez, Jason Hanna, and Phil Gast, “Gunman in Northern California Rampage Was Not Supposed to Have Guns,” CNN, November 15, 2017,; Damon Arthur, “Sheriff: Tehama Shooter Built His Own Illegal Guns,” Record Searchlight, November 15, 2017,[]
  9. Brad Brooks, “California School Shooting Shines Light on Murky ‘Ghost Gun’ World,” Reuters, November 22, 2019,[]
  10. Peter Hall and Pamela Lehman, “Suspect in Fatal Walmart Shooting, Banned from Buying Guns, Had Homemade One,” The Morning Call, May 13, 2018,[]
  11. Chad Pradelli, “Police: Exchange Student Charged in High School Threat Built Gun from Parts Bought Online,” ABC 7 News, April 2, 2018,[]
  12. 87 Fed. Reg. 24,652 (published April 26, 2022) (codified at 27 C.F.R. pts. 447, 478, 479).[]
  13. Id. at 24,735 (codified at 27 C.F.R. § 478.11).[]
  14. The rule defines “readily.” Id.; id. at 24,747 (codified at 27 C.F.R. § 479.11).[]
  15. An 80% frame or receiver, unlike a fully manufactured frame or receiver (which was treated as a “firearm” even before this rule), has not been fully machined, requiring additional machining to become a functional frame or receiver, but is sold in a nearly complete form.[]
  16. 18 U.S.C. § 922 (requiring federal firearm licensees to conduct background checks on a prospective purchaser before transferring a firearm).[]
  17. Id. at 24,735 (codified at 27 C.F.R. § 478.12).[]
  18. Id. at 24,747 (codified at 27 C.F.R. § 479.102).[]
  19. Id. at 24,734 (codified at 27 C.F.R. § 478.11).[]
  20. The rule defines “complete weapon.” Id.; id. at 24,747 (codified at 27 C.F.R. § 479.11).[]
  21. Id. at 24,746 (codified at 27 C.F.R. § 478.125(i) ).[]
  22. Id. at 24,735 (codified at 27 C.F.R. § 478.11).[]
  23. The rule does not require an unlicensed person to conduct a background check when selling a PMF. As such, federal law requiring only FFLs to conduct background checks is unaffected. Federal law does not require unlicensed sellers to conduct background checks on a potential buyer. Federal law does not require a person to possess a license to make a firearm for personal use or to make occasional sales of firearms.[]
  24. E.g., Philadelphia Code Tit. 10 § 10-2002 (prohibiting the manufacture of firearms or firearm parts using a 3D printer without a federal license to manufacture firearms).[]