An unknown number of guns are being built with the mechanisms, causing problems for the police and ATF officials. Photo: An ATF agent holds a generic unfinished receiver, back, and one that has been manufactured, front, at an ATF field office in Washington, on May 06, 2014. The ATF is trying to crack down on the trade in the makeshift guns by targeting shops and individuals who offer to turn the unfinished receivers into functional pieces for firearms. (Photo by Bill O'Leary/The Washington Post)

Maj. Matt O'Donnell of Glenelg, MD shields himself from rotor wash as Ospreys carrying the delegation of U.S. Secretary of Defense Leon Panetta leaves on March 14, 2012 at Forward Operating Base Shukvani, Afghanistan. Panetta is also scheduled to meet with President Karzai during his two-day visit to Afghanistan. The trip comes as the Taliban has vowed revenge following this past weekend's killing spree by a U.S. soldier who is accused of killing 16 civilians in Afghanistan. Most of those killed were children and women. (Photo by Scott Olson/Getty Images)

People pose for photographs in the wind during Typhoon Saola in Tseung kwan O, in Hong Kong on Saturday, September 2, 2023. Typhoon Saola made landfall in southern China before dawn Saturday after nearly 900,000 people were moved to safety and most of Hong Kong and other parts of coastal southern China suspended business, transport and classes. (Photo by Billy H.C. Kwok/AP Photo)

Democratic presidential candidate and US Vice President Kamala Harris reacts as she holds a photographer's camera while flying on Marine Two, on her way to O'Hare International Airport, Chicago, Illinois, on August 20, 2024. Harris is traveling to Milwaukee, Wisconsin, to speak at a campaign event. (Photo by Kevin Lamarque/Pool via AFP Photo)

The crowd watches as stunt pilots Melissa Pemberton, Jurgis Kairys and Skip Stewart of The Immortals fly past pyrotechnics as they perform at The Australian International Airshow on March 1, 2015 in Avalon, Australia. (Photo by Scott E. Barbour/Getty Images)

Azalea, whose Korean name is “Dalle”, a 19-year-old female chimpanzee, lights a cigarette at the Central Zoo in Pyongyang, North Korea on Wednesday, October 19, 2016. According to officials at the newly renovated zoo, which has become a favorite leisure spot in the North Korean capital since it was re-opened in July, the chimpanzee smokes about a pack a day. They insist, however, that she doesn’t inhale. (Photo by Wong Maye-E/AP Photo)

Kendall Jenner seen at Universal, NBC, Focus Features, E! Entertainment Golden Globes After Party Sponsored by Chrysler on Sunday, January 8, 2017, in Beverly Hills, Calif. (Photo by Eric Charbonneau/Invision for Focus Features/AP Images)

People wear face masks as they ride an E-scooter in the Old Elbe Tunnel in Hamburg, Germany, Thursday, October 15, 2020. To avoid the spread of the coronavirus the use of a face mask in the 117-year-old tunnel under the Elbe river is mandatory. (Photo by Michael Probst/AP Photo)