The Lake City Army Ammunition Plant, built during World War II, has long been operated for the federal government by private contractors. Over the past decade, a New York Times investigation found, the site has increasingly produced rounds for the commercial market as military demand has diminished.

The Army says the commercial business is meant to keep the factory in good working order so that military production can be quickly ramped up, while also reducing the cost of its ammunition. The current contractor, Olin Winchester, did not respond to inquiries from The Times. …

By reviewing annual reports, earnings-call transcripts and government documents, and interviewing more than 40 former employees and others with knowledge of Lake City’s operations, The Times was able to determine that the site, in Independence, Mo., had manufactured hundreds of millions of rounds for the commercial market every year since at least 2011. …

The vast majority of Lake City rounds sold by retailers have gone to law-abiding citizens, including hunters, farmers and target shooters. Some are drawn to them because they are made with the same materials and often to the same specifications as the military’s, while others see them as an authentic accessory for their tactical weapons and gear

But some Lake City rounds have been seized from drug dealers, violent felons, antigovernment groups, rioters at the U.S. Capitol and smugglers for Mexican cartels. They were confiscated from a man in Massachusetts who threatened to assassinate President Barack Obama and from a man at Los Angeles International Airport after he fired at a civilian and three T.S.A. agents, killing one.