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)

A silkmoth that has hatched out of its cocoon is seen at the Campoverde cooperative, Castelfranco Veneto, Italy June 4, 2015. Despite having wings, the adult moth cannot fly. Clusters of silkworms munch on piles of locally-grown mulberry leaves in a white marquee in Italy's northern Veneto region. They are nourishing hopes of a revival of Italy's 1,000 year-old silk industry. (Photo by Alessandro Bianchi/Reuters)

Alexo Carmona, 2, looks at Coco, a two-year-old pony, in downtown Havana, in this March 6, 2015 file photo. Nearly a quarter of a million people follow the Reuters Instagram account – and it's still growing fast. To mark the mid-point of 2015, Reuters has compiled the twenty most-liked pictures so far. This picture was 20th most popular. (Photo by Alexandre Meneghini/Reuters)

A boy runs as heavy rains and high waves brought by typhoon Linfa, locally named Egay, crash along a breakwater along Manila Bay at a slum area in Baseco, Tondo in Manila July 6, 2015. All shipping was ordered to remain in harbor and some flights were canceled in the northern Philippines, while schools were closed in the capital, Manila, on Monday due to flooding and landslides from a tropical storm, disaster officials said. Storm warnings were issued in at least 14 areas of the main Philippine island of Luzon as tropical storm Linfa moved slowly across the north of the Southeast Asian archipelago. It was carrying maximum wind gusts of 100 km per hour (60 mph). (Photo by Romeo Ranoco/Reuters)

Employees of a food stand take pictures of Titan, a robot created by England Cyberstein Robots, performing at the Danilovsly market in downtown of Moscow, Russia, 12 May 2014. Titan visited to Moscow to attend “Bal Robotov”, an interactive exhibition of the most recent advances in robotics which will be opened on 15 May in Artplay Moscow exhibition center. Titan worked alongside superstars including Will.i.am, Rihanna, Will Smith and Jackie Chan. (Photo by Sergei Ilnitsky/EPA)

President Barack Obama watches as Joey Hudy (L), 14, from Phoenix, Arizona pumps the Extreme Marshmallow Cannon he invented, while touring student science fair projects on exhibit in the State Dining Room at the White House February 7, 2012 in Washington, DC. Obama hosted the second White House Science Fair celebrating the student winners of science, technology, engineering and math (STEM) competitions from across the country. (Photo by Molly Riley-Pool/Getty Images)

“Rosslyn Chapel, properly named the Collegiate Chapel of St. Matthew, was founded on a small hill above Roslin Glen as a Roman Catholic collegiate church (with between four and six ordained canons and two boy choristers) in the mid-15th century. Rosslyn Chapel and the nearby Roslin Castle are located at the village of Roslin, Midlothian, Scotland”. – Wikipedia

Photo: The interior of Rosslyn Chapel on February 9, 2012 in Roslin, Scotland. Built between 1446 and 1484 it is a category A listed building, covered in ornate stonework and carvings of individual figures and scenes. People travel from all over the world to visit the chapel which many have described as an architectural wonder and a library in stone. Many theories, myths and legends associated with the Chapel have given it a unique sense of mystery and wonder. (Photo by Jeff J. Mitchell/Getty Images)

A boy carries a dog as he stands after a Peruvian police operation to destroy illegal gold mining camps in a zone known as Mega 14, in the southern Amazon region of Madre de Dios July 14, 2015. Peruvian police razed dozens of illegal gold mining camps at the edge of an Amazonian nature reserve this week, part of a renewed bid to halt the spread of wildcatting in a remote rainforest region. (Photo by Janine Costa/Reuters)