FN 15 M4 Military Collector 5.56 NATO 16in Matte Black Semi Automatic Modern Sporting Rifle - 30+1 Rounds - The FN 15 Military Collector Series M4 brings to market a military replica rifle made to FNs, and the U.S. military's exacting specifications. The semi-automatic rifle features a 16in, 1: 7in twist, button-broached, and chrome-lined barrel. The UID-labeled lower receiver is equipped with an ambidextrous selector switch, just like its select-fire big brother, the M4A1.