Under Half of Illegal Gun Cases Tracked by A.T.F. Were Involved in Black Market Sales

Four in 10 illegal gun cases tracked by the Bureau of Alcohol, Tobacco, Firearms and Explosives were involved in black market sales, including from shadow dealers who used a legal loophole to evade background checks, according to an analysis of firearms trafficking released on Thursday.

About another 40 percent of gun investigations initiated by federal officials centered on illegal “straw” purchases made by proxies hired by criminals, or other people prohibited from legally buying weapons for themselves because of drug use or mental illnesses.

The report, part of a broader effort by the Biden administration to make public previously undisclosed firearms data, offered an expansive portrait of the country’s growing illegal firearms market — including the origin of weapons and trafficking patterns.

The study is the third of four scheduled to be released. It covers about 10,000 A.T.F. investigations from 2017 to 2021 — a period that included the biggest surge in gun violence in decades. But it is likely to undercount more recent developments, such as the rapid proliferation of deadly homemade weapons known as “ghost guns,” federal officials said.

The White House is likely to use the new data to muster support for regulations closing a loophole that has allowed kitchen-table dealers, gun-show vendors and online sellers to avoid background checks required of 80,000 federally licensed dealers by claiming they are not primarily “engaged in the business” of firearms sales.

The proposed rule change is part of President Biden’s piecemeal push to enact a key policy goal — universal background checks — which congressional Republicans have repeatedly stymied. Some gun rights advocates have vowed to fight the measure, saying the vast majority of sellers are law-abiding citizens or collectors.