The M400-SDI X was designed to meet the highest standards of performance and reliability. From the rifle's full suite of ambidextrous controls to its proven mid-length gas system. Features fully Ambi Controls- safety, charging handle, bolt Catch & mag release; 2-Stage Matchlite Duo trigger; free floating M-LOK; mid-length direct impingement operating system and 6 position Magpul SL stock.