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)

First time gun owner, Jessie Palmieri holds a target she shot with a H&K VP9 9mm gun at the Ringmasters of Utah gun range, in Springville, Utah on December 18, 2015. (Photo by George Frey/Reuters)

A sticker is seen at the Rocky Mountain Guns and Ammo store in Parker, Colorado July 24, 2012. The killing of 12 people at a midnight screening of the new Batman movie in the Denver suburb of Aurora may spark a fresh round of soul-searching on America's relationship with guns but few predict any real change in the law. (Photo by Shannon Stapleton/Reuters)

A Ukrainian Army liaison officer Vira, 22, plays with her rat Malyi (Tiny) at her positions near a frontline, in Donetsk region, Ukraine, on March 8, 2024. (Photo by Inna Varenytsia/Reuters)

A man rides a motorcycle on a flooded street following heavy rains in Sanaa, Yemen on April 22, 2024. (Photo by Khaled Abdullah/Reuters)

Young recruits of the 72nd Chorni Zaporozhtsi Separate Mechanized Brigade of the Ukrainian Armed Forces attend an exercise, amid Russia's attack on Ukraine, in Kyiv region, Ukraine on April 5, 2025. Ukraine's Defence Ministry launched a recruitment drive for young people, 18- to 24-year-olds, to serve in the military for a year for the equivalent of about $24,000 and hefty bonuses. (Photo by Gleb Garanich/Reuters)

In this Friday, February 27, 2015 photo, an Israeli high-school senior preparing to join the Israeli military later this year participates in a privately run training camp for military combat fitness near Yakum, central Israel. With a mandatory three-year military service looming after graduation, teenage boys, and increasingly girls too, are gearing up for the draft, getting into shape and trying to improve their chances of acceptance into elite combat units. (Photo by Oded Balilty/AP Photo)

Sergey, one of the participants of PARTISAN courses, poses for a portrait in an abandoned building in Olgino, St. Petersburg, Russia on November 23, 2016. Sergey came to St. Petersburg from the city of Cheliabinsk to attend an intensive seven-day program. Sergey is a businessman, a traveller and a blogger. His another passion are “men's hobbies”, that's why he participated in the paramilitary courses. (Photo by Alexander Aksakov/The Washington Post)