This carbine comes with the good stuff - all of it - pre-installed. Like a free-floating M-LOK handguard, which promotes accuracy and handling. Or a quality grip and premium, 6-position buttstock with integral QD points. The M400 PRO comes standard with AMBI controls. The Enhanced SIG Trigger on the M400 PRO enables the shooter to extract excellent accuracy from the rifle. Lightweight 16'' nitride barrel that is equipped with a SIG Micro-light Gas Block.