Manhattan Mass Shooter used AR-15 Variant

The shooter who attacked a Park Avenue office building and killed four people used a commercial, semiautomatic version of an M4 rifle, a shorter version of the M16/AR-15 rifle developed by Eugene Stoner. As discussed in American Gun, the military version of the M4 rifle, which uses the same ammunition as an AR-15/M16, has been used by U.S. troops for years. Commercial versions, which cost as little as a few hundred dollars, have become more popular among civilians in recent years.