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)

A protester wearing improvised protective headgear walks away from a cloud of tear gas on July 18, 2021 in Bangkok, Thailand. Student protesters called for a demonstration demanding the resignation of Thailand Prime Minister Prayuth Chan-o-Cha, despite a ban on gatherings because of the country's current Covid-19 outbreak, and folded a demand for better action in combating the virus into their demands. (Photo by Sirachai Arunrugstichai/Getty Images)

A cat sits underneath lanterns displayed at Tai O fishing village on September 07, 2022 in Hong Kong, China. Hong Kong prepares ahead to celebrate the mid-autumn festival which is an occasion for a children's night out and family gathering with the customs of moon contemplating, a procession of star and moon-shaped lanterns, lion dance, as well as holding parties with moon cakes and fruits. (Photo by Anthony Kwan/Getty Images)

In this photo provided by the Florida Keys News Bureau, Maddie Miller, of Tampa, Fla., raises her head during the World Famous Key Lime Pie Eating Championship Tuesday, July 4, 2023, in Key West, Fla. The gooey competition, whose entrants are forbidden to use their hands, has become a subtropical alternative to Nathan's Famous Fourth of July hot dog eating contest in New York City. (Photo by Rob O'Neal/Florida Keys News Bureau via AP Photo)

American model and actress Emily O'Hara Ratajkowski attends the Jacquemus Spring Summer 2020 show on June 24, 2019 in Valensole, France. (Photo by Arnold Jerocki/Getty Images)