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)

Hamar women dance before a bull jumping ceremony in Ethiopia's southern Omo Valley region near Turmi on September 19, 2016. The Hamar are a Nilotic ethnic group in Ethiopia. The construction of the Gibe III dam, the third largest hydroelectric plant in Africa, and large areas of very “thirsty” cotton and sugar plantations and factories along the Omo river are impacting heavily on the lives of tribes living in the Omo Valley who depend on the river for their survival and way of life. (Photo by Carl De Souza/AFP Photo)

In this October 6, 2018, photo, a craftsman makes daggers or “Jambiyya” in Yemeni Arabic, made out of remains of missiles, at his workshop, in Hajjah, Yemen. Missiles raining on Yemen from the jets of the Saudi-led coalition fighting Houthi rebels are killing thousands of civilians and militiamen alike, but amid crashing economy, some Yemenis see the bright side of it: they make daggers out of the fragments of the missiles for ordinary men traditionally wear for prestige and a show of courage. (Photo by Hammadi Issa/AP Photo)

Lukas Michul, a member of the “dream walker” group jumps from atop the rugged rocks overlooking the azure waters of Navagio beach, one of the Greece's most renowned leisure spots on the popular tourist island of Zakynthos on June 23, 2014. This is rope jumping – part diving, part rock climbing, with a touch of engineering. The aim of the project is to dream jump in 80 places with most ravishing nature and architecture all over the world .They plan to stage their next leaps at a cave complex in Croatia, a French viaduct, skyscrapers in Las Vegas and Johannesburg, and the Grand Canyon. (Photo by Louisa Gouliamaki/AFP Photo)

In this February 28, 2015 photo, teammates struggle to lift a bull off the trapped leg of a charro, during the bull riding event at a charreada in Mexico City. National Charros Association President Manuel Basurto Rojas said: “We in charreria are taking things into our own hands. We have codes, we have rules, for how to treat the animals. On the other hand, there is a lot of danger involved for the men doing these tricks”. (Photo by Rebecca Blackwell/AP Photo)

In this June 16, 2017 photo, Batel Delciner, 23, removes wood from a furnace to lower the heat cooking sugar juice at the Ti Jean distillery, which produces clairin, a sugar-based alcoholic drink, in Leogane, Haiti. The broth is cooked for about four hours after a fermentation period of four to eight days. (Photo by Dieu Nalio Chery/AP Photo)

Elfyn Evans of Great Britain and Daniel Barritt of Great Britain compete in their M-Sport WRT Ford Fiesta RS WRC during Day One of the WRC Australia on September 11, 2015 in Coffs Harbour, Australia. (Photo by Massimo Bettiol/Getty Images)

Iranian Shiite Muslim women gather around a bonfire after rubbing mud on their body during the “Kharrah Mali” (Mud Rubbing) ritual to mark the Ashura religious ceremony in the city of Khorramabad, some 470 kms southwest of Tehran, early in the morning on October 1, 2017. “Khrreh Mali” or “Mud Rubbing” is a ritual that is held in the city of Khorramabad every year to commemorate the seventh century slaying of Prophet Mohammed' s grandson Imam Hussein, in which Iranian men roll over in mud and dry themselves by gathering around the bonfires before flagellating themselves. (Photo by Atta Kenare/AFP Photo)