France's Typhaine Solde competes in the women's long jump - T64 finals of the Tokyo 2020 Paralympic Games at the Olympic Stadium in Tokyo on August 28, 2021. (Photo by Kim Price/CSM/Rex Features/Shutterstock)

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)