Sig Sauer M400 Sdi 5.56 16 Xseries Blk Tele 30Rd

The Sig Sauer M400 SDI 5.56 is a modern patrol rifle built for shooters who need a dependable, ready-to-use platform for defense, training, or the range. This 16-inch carbine arrives fully configured with a ROMEO5 GENII red dot sight, FOXTROT-MSR tactical light, and vertical foregrip—no additional optics or mounting required. Sig Sauer's development team drew directly from feedback by professional instructors at the SIG SAUER Academy to ensure the M400 SDI meets real-world reliability and performance standards that serious operators expect.

The rifle's backbone is a free-floating 16-inch chrome-moly barrel with a 1:7 twist rate, tuned for the 5.56 NATO round and fitted with a SIG flash hider-compensator. The action runs on a mid-length direct impingement system with a low-profile gas block, delivering consistent cycling and control. A SIG 2-Stage Matchlite Duo flat-trigger breaks cleanly, while fully ambidextrous controls—safety, charging handle, bolt catch, and release—let you operate the rifle naturally from either shoulder. The 6-position Magpul MOE-SL stock lets you dial in your length of pull, and the reduced-angle grip fits most hands comfortably.

The M400 SDI's free-floating M-LOK forend is built for accuracy and modularity. It ships with three M-LOK rail covers to keep the handguard clean, and the top Picatinny section accepts standard optics and mounting systems if you ever want to swap your setup. The included ROMEO5 GENII sight features a crisp 1 MOA dot with over 40,000 hours of battery life thanks to SIG's motion-activated MOTAC design, plus IPX7 waterproofing and fully multicoated optics for performance in any light. The FOXTROT-MSR light delivers 1,250 lumens and 33,000 candela for low-light target acquisition. One 30-round polymer magazine and a vertical foregrip come standard. Weighing 8.0 pounds and measuring 36.5 inches overall, this is a carbine you can actually shoot all day.

Key Features

• Pre-installed ROMEO5 GENII red dot with 1 MOA dot and 40,000+ hour battery life
• FOXTROT-MSR full-size tactical light: 1,250 lumens, 33,000 candela
• Vertical foregrip included for control and handling
• Free-floating M-LOK forend with rail covers for accuracy and modularity
• SIG 2-Stage Matchlite Duo trigger with flat trigger shoe
• Chrome-moly steel barrel, 1:7 twist, threaded 1/2 in-28 for suppressors or muzzle devices
• Mid-length direct impingement with low-profile gas block
• Fully ambidextrous controls for left and right-handed shooters
• 6-position Magpul MOE-SL adjustable stock
• Includes one 30-round AR-15 magazine

Specifications

Frequently Asked Questions

Is the M400 SDI ambidextrous?

Yes. The safety lever, charging handle, bolt catch, and release are all fully ambidextrous, so left-handed and right-handed shooters can operate the rifle naturally from either shoulder.

What sights and light come with this rifle?

The M400 SDI ships with a ROMEO5 GENII red dot sight pre-installed on the upper receiver and a FOXTROT-MSR full-size tactical light mounted on the rail. Both are ready to shoot out of the box. A vertical foregrip is also included.

Can I suppress this rifle?

Yes. The barrel is threaded 1/2 in-28 tpi with a tapered shoulder, which accepts standard suppressors and muzzle devices. The rifle also includes a SIG flash hider-compensator.

What magazine capacity comes with the rifle?

One 30-round AR-15 compatible polymer magazine is included.

Is the barrel free-floated for accuracy?

Yes. The M400 SDI features a free-floating M-LOK forend, which isolates the barrel from the handguard and helps maximize accuracy. The forend also ships with three M-LOK rail covers.