|Americans who know nothing else about firearms are all too familiar with the name AR-15. It’s the semi-automatic weapon that murderers have used in many of the most notorious and highest-casualty gun killings of recent years: Aurora, Colorado. Newtown, Connecticut. Orlando, Florida. San Bernardino, California. Now, with modified versions, in Las Vegas, Nevada, and Sutherland Springs, Texas … A little bullet pays off so much in wound ballistics. That is what people who choose these weapons know.