Authorities say they've charged 10 people who were producing homemade, untraceable handguns and rifles in Hollywood.
The arrests were announced Thursday by the Bureau of Alcohol, Tobacco, Firearms and Explosives and Los Angeles police.
During a six-month undercover operation, detectives and federal agents purchased dozens of so-called "ghost guns."
LAPD Cmdr. Blake Chow said they face a total of 47 felony counts.
Ghost gun kits can be sold legally over the internet without the kind of background check required for traditional gun purchases. It's legal to build a gun in a home or a workshop.
But authorities say they are increasingly being used in crimes.
Federal authorities have been drawing attention to the dangers posed by "ghost guns," which contain no registration numbers that can be used to trace them.
MICHAEL BALSAMO, Associated Press
