Ghost guns, which include firearms assembled from kits or made with 3D printers, are untraceable by law enforcement and often undetectable by metal detectors. These guns pose a grave threat to public safety, and people who are legally prohibited from owning firearms are able to create them without consequences in most states. Legislators should act immediately to pass laws regulating the production and distribution of ghost guns before they become more widespread.


When American gun laws were written, legislators assumed that firearms would either be imported from abroad by dealers or manufactured domestically by professional gun manufacturers. In recent years, there has been an increasing number of efforts to circumvent these laws by exploiting the loopholes that result from that assumption. Selling gun parts and components that can easily be used to build a firearm is one such loophole since buyers of unfinished gun parts or components are not required to undergo a background check. Similarly, other federal and state laws that regulate gun sales or purchases often do not apply to unfinished parts and components.

Self-assembled firearms—which can be built from kits or 3D printed—are referred to as ghost guns because they do not come with a serial number and are untraceable. 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 2017 alone, ATF conducted more than 408,000 traces.1

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, to determine the chain of custody from the gun itself.

Furthermore, these guns may be produced largely or even entirely from plastic, which can render them undetectable by traditional 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.

Making Untraceable and Undetectable Guns

Some untraceable guns are assembled from parts purchased online. Under federal law, only a “frame” or “receiver” (the key component that houses the firing mechanism) of a firearm must carry a serial number. Anyone purchasing a receiver is subject to a background check. Creative online retailers have devised a way to skirt federal serialization and background check requirements by marketing “unfinished” frames or receivers that can be turned into fully functioning frames or receivers with minimal tools or effort. Pre-programmed milling machines are available online that will produce a fully functional receiver from an unfinished receiver with the press of a button. Sold in this form, these unfinished frames or receivers are not required to carry serial numbers and can be sold without a background check according to the standards set by ATF.

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.

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.”2 In July 2018, the Los Angeles Police Department broke up a brazen gang-trafficking enterprise in Los Angeles.3 Individuals have been caught manufacturing and selling untraceable guns in locations across the country.4 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.5

Ghost guns have also been used in multiple recent 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.6 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.7

Other tragedies have been narrowly averted. In Pennsylvania, a police officer responding to a call outside Philadelphia shot and killed a convicted felon who had threatened to shoot the officer with a homemade gun made with parts he ordered online.8 The following month, police averted a school shooting outside Philadelphia by a student who had assembled an untraceable gun he had purchased online.9

Summary of Federal Law

Federal law prohibits some undetectable firearms. The Undetectable Firearms Act requires that all firearms be detectable by metal detectors “after removal of grips, stocks, and magazines.”10 It also requires that all major components of firearms—defined to include “the barrel, the slide or cylinder, or the frame or receiver”—must be detectable by x-ray machines.11

However, the Undetectable Firearms Act does not specify what portion of the firearm must be detectable by a metal detector. This could allow an individual to create a mostly plastic but technically compliant firearm, using a 3D printer or other technology, that contains metal in an extraneous part of the firearm that could be removed prior to entering a security area.

Summary of State Law

Two states have enacted comprehensive laws to address the problem of undetectable and untraceable guns. Further restrictions have also been implemented at the local level.12


California’s ghost gun law, which was enacted in 2016 and first became effective in July 2018, imposes several requirements on anyone who manufactures or assembles a firearm:

  • A self-assembled firearm must contain a unique serial number provided by the California Department of Justice (DOJ).13 If the firearm is made from plastic, the serial number must be engraved or affixed on a piece of metal large enough to be detected by metal detectors and embedded within the plastic.14
  • The individual must provide information about the newly serialized firearm, including the identity of the owner of the firearm, to DOJ.15 Firearms manufactured or assembled pursuant to these provisions are for personal use only and cannot be sold or transferred.16
  • Anyone in possession of an unserialized firearm who manufactured a firearm before the law went into effect in July 2018 must apply to the DOJ for a serial number and must serialize the firearm, or must surrender the unserialized firearm to law enforcement.17
  • The law also expressly prohibits individuals or companies from knowingly allowing, facilitating, aiding, or abetting the manufacture or assembly of a firearm by individuals prohibited from possessing a firearm under state law.18
  • In addition, self-assembled firearms must be compliant with the requirements of California’s Unsafe Handgun Act, which requires that handguns meet certain safety specifications. See our Design Safety Standards for Handguns in California policy summary for a comprehensive discussion of the Unsafe Handguns Act.

New Jersey

In 2018 New Jersey enacted the most comprehensive ghost gun law in the country. The new law:

  • Prohibits the purchase or acquisition of parts, including unserialized frames or receivers, “from which a firearm without a serial number may be readily manufactured or otherwise assembled.”19
  • Prohibits using a 3D printer to produce a firearm or firearm components, including a receiver or magazine, unless the acquirer is registered or licensed by the state as a firearm manufacturer or dealer.20
  • Prohibits the distribution of computer code capable of manufacturing firearms and firearm components using a 3D printer to anyone but a manufacturer licensed under state law.21
  • Expands the federal prohibition on undetectable firearms, requiring that the major components of a firearm must be detectable by security screening devices.22

Key Legislative Elements

The features listed below are intended to provide a framework from which policy options may be considered. Any jurisdiction considering new legislation should consult with counsel.

  • Prohibit untraceable guns by requiring that 3D-printed firearms and unfinished frames and receivers carry a serial number.
  • Prohibit the indiscriminate distribution of code to produce 3D-printed guns—for example, only allow distribution to a specific individual after a background check has been conducted, or only allow distribution to licensed firearm manufacturers.
  • Prohibit undetectable firearms by requiring that all operable firearms be detectable by standard screening systems.
  • Require a background check before transferring an unfinished frame or receiver.
  • Require a license to manufacture or assemble a firearm using unfinished materials or a 3D printer.
  1. Bureau of Alcohol, Tobacco, Firearms and Explosives, “ATF By the Numbers,” June 14, 2018, ⤴︎
  2. 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, ⤴︎
  3. Richard Winton, L.A. Gangs Stockpile Untraceable ‘Ghost Guns’ that Members Make Themselves, Los Angeles Times, July 6, 2018, ⤴︎
  4. 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, ⤴︎
  5. Maxwell Reil, “Man indicted after selling ‘ghost gun’ in Hammonton,” Atlantic City Press, April 13, 2018, ⤴︎
  6. Robert Cavnar, “Santa Monica Shooter Built His Gun From Parts He Bought Online,” Huffington Post, June 15, 2013, ⤴︎
  7. 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, ⤴︎
  8. Peter Hall and Pamela Lehman, “Suspect in Fatal Walmart Shooting, Banned from Buying Guns, Had Homemade One,” The Morning Call, May 13, 2018, ⤴︎
  9. Chad Pradelli, “Police: Exchange Student Charged in High School Threat Built Gun from Parts Bought Online,” ABC 7 News, April 2, 2018, ⤴︎
  10. 18 U.S.C. § 922(p)(1)(A). ⤴︎
  11. 18 U.S.C. § 922(p)(1)(B), (p)(2)(B). ⤴︎
  12. E.g., Philadelphia Code Tit. 10 § 10-2002 (prohibiting the manufacture of firearms or firearm parts using a 3D printer unless one has a federal license to manufacture firearms). ⤴︎
  13. Cal. Penal Code § 29180(b)(1), id. § 29180(b)(2)(A). ⤴︎
  14. Id. § 29180(b)(2)(B). ⤴︎
  15. Id. § 29180(b)(3). ⤴︎
  16. Id. § 29180(d). ⤴︎
  17. Id. § 29180(c). ⤴︎
  18. Id. § 29180(f). ⤴︎
  19. N.J. Stat. Ann. § 2C:39-9(k). ⤴︎
  20. N.J. Stat. Ann. § 2C:39-9(l)(1). ⤴︎
  21. N.J. Stat. Ann. § 2C:39-9(l)(2). ⤴︎
  22. N.J. Stat. Ann. § 2C:39-1(ii); id. § 2C:39-9(m). ⤴︎