Sig Sauer M400-SDI XSeries 5.56mm NATO 16in Anodized Black Semi Automatic Modern Sporting Rifle - 30+1 Rounds - SIG'S new M400 SDI Series of rifles designed from the ground up to deliver maximum performance and reliability. The M400 X-features a free-floating M-LOK handguard, Magpul SL-K 6-position telescoping stock, Sig Flat Match Grade trigger, 16in Chrome Moly barrel, and a 7075 T-6 aluminum receiver with a black hardcoat anodized finish.