Thomas Matthew Crooks used an AR-15 in his attempt to assassinate Donald Trumpover the weekend, and there are currently 24 million of these deadly semi-automatic weapons in the United States, RadarOnline.com can reveal. The gun was designed in the 1950s and meant to be used on the battlefield but has been responsible for almost a quarter of the country’s mass shootings, including at a Uvalde elementary school in Texas in May 2022, in which 21 people – 19 of them children, were killed. The semi-automatic rifle has grown in popularity since the ending of the Assault Weapons Ban in 2004. It’s als…