SIG SAUER M400 SDI X Pistol 5.56 NATO 11.5 Inch

Description

The M400 SDI X is built around a compact pistol-format AR platform suited to shooters who want a short, maneuverable carbine-style build without compromising on terminal performance. The 5.56 NATO chambering keeps the ammunition selection broad, from light varmint loads to heavier bonded defensive rounds, and the 1:7-inch twist rate stabilizes the heavier end of that spectrum well — bullets in the 62- to 77-grain range will seat better into the rifling and maintain coherent flight than they would in the slower-twist barrels common on older surplus or budget builds.

The 11.5-inch barrel sits at a point where the gas port has less dwell time to work with than a longer carbine, which affects the gas impulse that cycles the action. Sig engineered the SDI around this constraint, and the result is a platform that cycles reliably without the violent over-gassing that can plague shorter barrels adapted from longer-barrel specifications. The Black FNC barrel finish offers corrosion resistance while keeping the surface hard enough to stand up to friction from field use.

The optic-ready configuration means no iron sight hardware is eating rail space or adding weight above the receiver — the expectation is that the shooter will mount a red dot or low-power variable, and the flat top leaves that choice entirely open. The threaded muzzle at 1/2×28 accepts a wide range of standard flash hiders, compensators, or suppressors. One 30-round magazine is included. The thumb safety layout follows the standard AR ergonomic pattern, keeping manual of arms consistent for anyone already trained on that platform.

Shipping and availability: This item cannot be shipped directly to California, Rhode Island and Washington. Check your state and local requirements before ordering. This item must ship to a licensed FFL dealer for transfer.