Muhannad al-Kadiri (R),18, and Ibrahim Eid, 16, demonstrate their Parkour skills over a military vehicle in the rebel-held city of Inkhil, west of Deraa, Syria, February 4, 2017. (Photo by Alaa Al-Faqir/Reuters)

Two guards perform an execution in China, one holding the gun, the other holding a mask over the victim's face. (Photo by General Photographic Agency/Getty Images). Circa 1925

The battleship USS Iowa fires its 16-inch guns during duty in the Persian Gulf on December 16, 1987. In 1943, the Iowa ferried President Franklin Roosevelt home from the Teheran Conference, where post-WW II leaders divided up the world. The ship fought battles from the South Pacific to Korea and escorted convoys through the Persian Gulf. Forty-seven sailors died atop its deck when an explosion ripped through a gun turret. Now, the new port for the retired USS Iowa just might be the home of California's annual asparagus festival, the gritty agriculture port town of Stockton on the San Joaquin River, about 80 miles inland from San Francisco. (Photo by Eric Risberg/AP Photo)

Seized plastic handguns which were created using 3D printing technology are displayed at Kanagawa police station in Yokohama, south of Tokyo, in this photo taken by Kyodo May 8, 2014. Yoshimoto Imura became the first man to be arrested in Japan for illegal possession of two guns he created himself using 3D printing technology, Japanese media said on Thursday. The 27-year-old, a college employee in the city of Kawasaki, was arrested after police found video online posted by Imura claiming to have produced his own guns. Gun possession is strictly regulated in Japan. Police raided Imura's home and found five guns, two of which could fire real bullets, Japanese media said. (Photo by Reuters/Kyodo)

A soldier poses with a Hythe Mk III Gun Camera during training activities at Ellington Field, Houston, Texas in April of 1918. The Mk III, built to match the size, handling, and weight of a Lewis Gun, was used to train aerial gunners, recording a photograph when the trigger was pulled, for later review, when an instructor could coach trainees on better aiming strategies. (Photo by Harry Kidd/WWI Army Signal Corps Photograph Collection via The Atlantic)

A military police officer aims his gun to a demonstrator during a protest in Brasilia, Brazil, Tuesday, April 7, 2015. The officer had picked up a bottle that was thrown towards them but did not fire his gun and backed away. Thousands of workers have staged rallies in 12 cities across Brazil to protest against a proposed law that would allow companies to outsource their labor force. (Photo by Eraldo Peres/AP Photo)

Members of the Al-Baraa bin Malek batallion, part of the Free Syria Army's Al-Fatah brigade, duck to the ground as they pull a man (R) who was shot by a sniper twice in the Bustan al-Basha district of the northern city of Aleppo on October 20, 2012. (Photo by Javier Manzano/AFP Photo)

Syrians try to rescue a dead body under the debris of a collapsed building after Syrian and Russian army carried out an airstrike on opposition controlled residential area at Merce neighborhood of Aleppo, Syria on September 23, 2016. (Photo by Jawad al Rifai/Anadolu Agency/Getty Images)