WASHINGTON — President Biden celebrated the adoption of a federal rule in August that cracked down on the online sale of untraceable components for weapons known as ghost guns as a major step in stemming gun violence. But the rule has done little to stop the sale of key parts used to make deadly homemade firearms, according to officials and gun control groups.
The rule, among the most significant executive actions Mr. Biden has taken on a core campaign promise, clarified the definition of a firearm under federal law to better regulate modern semiautomatic weapons. That in turn paved the way for regulating ready-made kits, which include all the parts needed to assemble a workable firearm in under an hour.
The move was a centerpiece of the administration’s broader initiative to address the proliferation of illegal weapons driving an increase in mass shootings and violent crime — an effort highlighted by the passage of Mr. Biden’s sweeping, if limited, bipartisan gun deal in June. But because the rule was created through executive action, rather than a statute validated by Congress, it has given companies confidence that they can keep selling individual gun parts.
Dozens of online retailers are still selling core components used to make ghost guns, also known as privately manufactured firearms, according to research by Everytown for Gun Safety, an advocacy group founded by Michael R. Bloomberg, the former mayor of New York City. Many have adopted the narrowest possible interpretation of the rule, continuing to sell so-called 80 percent frames and receivers, which require simple alterations to become operational.
The Bureau of Alcohol, Tobacco, Firearms and Explosives, the agency responsible for enforcing gun laws, has been reluctant to target vendors who sell those parts out of concern that doing so would prompt a legal backlash — even though Mr. Biden’s allies are pushing the administration to take a much more aggressive stance.
“The problem is it’s a regulation, not a statute, so there’s only so much A.T.F. can do,” said Adam Winkler, a law professor at the University of California, Los Angeles, who studies the legal and constitutional issues around gun policy.
“There are clear limits, and they risk losing in court if they push it too far,” he added. “That’s why you now see companies that used to market the kits simply switching over to selling the components separately, and letting the buyers assemble their own kits.”
In recent months, gun control groups and Democrats in Congress have pressured Steven M. Dettelbach, the A.T.F.’s new director, to act more decisively. In October, Senators Richard Blumenthal and Christopher S. Murphy, Democrats of Connecticut, along with 12 other senators, wrote Mr. Dettelbach asking for a detailed update on enforcement of the new law. Gun safety groups have enlisted Democratic legislators to nudge Mr. Dettelbach in weekly phone calls.
But A.T.F. officials have cautioned that pushing the limits of the rule with a range of other changes, like requiring federally licensed firearms dealers to place serial numbers on homemade guns bought from do-it-yourself sellers, could jeopardize it entirely. The rule also compels gun dealers to improve their record-keeping procedures.
Many gun control groups believe the A.T.F. is being too cautious, citing the first wave of mostly unsuccessful court challenges to the regulation as proof that an expanded crackdown could be legally viable.
“The sale of ghost guns is finally illegal, but you wouldn’t know it for all the companies still selling untraceable firearms to anyone with a credit card and a desire to avoid a background check,” said John Feinblatt, the president of Everytown.
“President Biden issued a muscular regulation to stop the sale of ghost guns, but now it’s time for D.O.J. and A.T.F. to use the strength he gave them to keep Americans safe,” he added.
The bureau, in consultation with senior leaders at the Justice Department, is hashing out a circular to clarify what the new rule means for the sale of components used to produce Glock-style pistols, the weapon of choice for many criminals seeking an untraceable firearm. The guidance is expected to be made public before the end of the year.
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A similar letter governing AR-15-type rifles, which represent a much smaller percentage of homemade firearms used in crimes, was released in September. It did not signal significant new restrictions on the sale of components, to the frustration of gun safety groups.
But the A.T.F. seems likely to continue its deliberate approach — analyzing court decisions for clues on how hard they can push, and monitoring online vendors whose marketing materials may run afoul of a new rule that requires kits to be given serial numbers like over-the-counter firearms, according to officials.
It is not clear if the new guidelines on handguns will target the sale of online parts. But A.T.F. officials have told members of Congress they worry that doing so would almost certainly elicit court challenges from gun rights groups arguing that such action violates the Gun Control Act of 1968, which allows the construction of firearms for their personal use without submitting to background checks or applying serial numbers.
“The Constitution does not authorize the federal government to prevent you from making your own firearm,” Representative Thomas Massie, Republican of Kentucky, said on Twitter shortly before the rule was announced in April. “This a fact that has been recognized for 200+ years.”
But A.T.F. officials are increasingly confronting challenges posed by rapidly evolving technologies that regulators have not had to confront in the past, such as 3-D printing of gun parts and the online marketing and sale of weapons on social media.
Ghost guns, which have gone from a novelty to a national menace in the past several years, are emblematic of those challenges.
They are increasingly becoming the lethal weapon of easy access for those legally barred from buying or owning guns around the country, especially in states with stringent gun control laws. In 2021, the Justice Department reported that law enforcement agencies had recovered 19,300 homemade guns, about five times the number confiscated or found at crime scenes in 2018.
The problem has reached epidemic proportions in California, according to local and federal law enforcement officials in Los Angeles, Oakland, San Diego and San Francisco. Over the past several years, the officials said, ghost guns accounted for 25 to 50 percent of firearms recovered at crime scenes. The vast majority of suspects caught with them were legally prohibited from having guns.
The struggle to translate Mr. Biden’s emphatic declarations on ghost guns has fallen to Mr. Dettelbach, the first permanent A.T.F. director confirmed by the Senate in nearly a decade.
During his first several months in office, he has quietly reorganized the bureau’s senior leadership, and sought to bolster morale among career staff.
Mr. Dettelbach, a former U.S. attorney in Ohio, has also prioritized investigations into so-called straw purchase rings organized to buy weapons that are later sold to criminals and federally licensed gun dealers who violate the law.
Many liberal-leaning states and localities have passed their own laws to regulate ghost guns after a series of mass shootings involving them. At least 10 states have done so and a handful of cities, including New York, Washington and Los Angeles, have sued ghost gun manufacturers over attacks carried out using such weapons.
But the powerful gun lobby strongly opposed the new federal rule, and several conservative legal groups have already challenged it, arguing that it violates existing firearms laws and Second Amendment protections.
In August, 17 states and a coalition of gun rights activists sued the Biden administration in federal court in North Dakota. That suit was rejected, but other challenges, including a lawsuit in a federal court in Texas, remain unresolved after a judge issued a temporary restraining order against the rule’s implementation.