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)

Armed women attend a rally to show support to the Houthi movement in Sanaa, Yemen January 13, 2018. (Photo by Khaled Abdullah/Reuters)

Visitors run away as waves caused by a tidal bore surge past a barrier on the banks of Qiantang River, in Hangzhou, Zhejiang province August 13, 2014. (Photo by Reuters/Stringer)

American Yoga teacher Dashama poses on a Yoga-board during a preview of the 46th International Boat Fair in Duesseldorf January 16, 2015. The BOOT 2015 watersports fair, with more than 1,600 international exhibitors will run in Duesseldorf from January 17 to January 25. (Photo by Ina Fassbender/Reuters)

A woman doing yoga at a fountain, in downtown Stuttgart, Germany, Thursday, June 22, 2017. Weather forecasts predict hot summer weather as well as thunderstorms for some parts of Germany. (Photo by Marijan Murat/DPA via AP Photo)

A goat hops from student to student during a goat yoga class at the University of Tennessee on August 25, 2022 as part of welcome back week. The session was organised by Goat Yoga Nashville. (Photo by Matt Hamilton/Chattanooga Times Free Press via AP Photo)

An Afghan girl rides a horse at the beach in Karachi, Pakistan, 07 September 2020. (Photo by Rehan Khan/EPA/EFE)

A girl wearing a face mask as a precaution against the coronavirus walks past a display of garments at a market in Bengaluru, India, Saturday, January 9, 2021. India will kick off the coronavirus vaccination drive on Jan. 16 to stem the pandemic in the world's second-most populous country. A Health Ministry statement says that priority will be given to the healthcare workers and the frontline workers, estimated around 30 million. (Photo by Aijaz Rahi/AP Photo)