The Bureau of Alcohol, Tobacco, Firearms, and Explosives performed fewer inspections of federally licensed firearms dealers, or FFLs, in 2015 than in any year in the past decade.

According to a new agency report, federal investigators inspected just 8,696 of the country’s nearly 140,000 licensed firearm dealers last year — 6.3 percent of the total.

The new figures signify the lowest rate of inspections since 2005, when investigators visited just 4.9 percent of dealers.

The ATF issues licenses to sell firearms to brick and mortar retail stores, pawnbrokers, manufacturers, importers, and collectors. Licensed sellers are required to perform background checks on all gun sales and transfers.

The ATF is not legally required to inspect every licensed dealer in a given year, but the agency sets a goal of inspecting each vendor with a license at least once every three to five years. The agency routinely falls well short of its self-imposed benchmark: A 2013 investigation by the ATF’s Office of the Inspector General found that just 42 percent of dealers had been inspected in the past five years. Since 1975, the agency has never inspected more than 10.6 percent of dealers in a given year.

In 2015, the agency had 811 investigators devoted to inspections — or approximately one for every 172 license holders. One reason the ATF has historically struggled to keep up with inspections: The number of licensees keeps going up. There were nearly 35,000 more licensed dealers last year than a decade ago. The number of investigators has not increased at the same pace.

An ATF spokeswoman said the agency was not immediately prepared to comment.

Some experts on gun dealing and trafficking say the declining rate of inspections could implicitly encourage licensed dealers to neglect best business practices. “It sends the signal they can get away with not keeping track of inventory, not keeping records, even selling weapons out the back door,” Jay Wachtel, a retired ATF agent who specialized in gun trafficking, tells The Trace.

In 2015, an ATF inspection uncovered nearly 3,000 unreported lost weapons at a single gun store in Arkansas. The finding earned Arkansas — a relatively small state with far fewer gun dealers than neighboring Texas — the distinction of the state with the most weapons lost or stolen from licensed dealer.

Lost weapons often end up in criminal hands, says Chelsea Parsons, a policy analyst at the Center for American Progress who has studied the ATF.

“Without regular, thorough inspections, these businesses are allowed to operate with very few checks in place to make sure that they are not diverting guns into the illegal market, either through negligence or malfeasance,” she says.