Sig Sauer M400 SDI XSeries 5.56 NATO AR-15 Rifle – FDE Finish, Ambidextrous Controls, 16-Inch Threaded Barrel
The M400 SDI XSeries brings Sig Sauer’s duty-ready engineering to an upgraded AR-15 platform. Released in 2024 after collaboration with Sig Sauer Academy instructors, this rifle blends a chrome-moly 16-inch barrel, fully ambidextrous controls, and a flat-face Matchlite Duo trigger into a lightweight, Flat Dark Earth–finished package. A dual-clamp free-float M-LOK handguard and mid-length gas system round out a build designed for precise handling and reliable performance.
Condition
Overall Condition: Excellent – showing only faint signs of prior use or handling.
Bore Condition: Excellent – clean, mirror finish, no signs of wear.
Bore Rifling: Excellent – sharp lands and grooves.
Specific Condition Notes: This rifle exhibits light handling marks on exterior surfaces but no functional or cosmetic defects that affect performance.
What’s Included
- SIG Sauer factory cardboard rifle box
- SIG Sauer manual and documentation pack
- Three bagged SIG Sauer QD sling swivel mounts
- Two 30-round Magpul PMAG magazines
- One 10-round steel AR-15 magazine
The heart of the SDI XSeries is its 16-inch chrome-moly barrel with a 1:7 twist, optimized for modern 5.56 NATO loads. The barrel is threaded 1/2-28 for easy addition of muzzle devices and protected by a free-float aluminum handguard that extends full Picatinny rail coverage from receiver to muzzle.
Fully ambidextrous controls—magazine release, safety selector, and charging handle—let right- and left-handed shooters run the rifle without compromise. The flat-face Matchlite Duo two-stage trigger delivers a crisp, predictable break ideal for both precision and rapid fire.
Built on 7075-T6 aluminum receivers coated in durable Flat Dark Earth Cerakote, the rifle pairs a six-position collapsible stock with a reduced-angle pistol grip for comfortable, repeatable ergonomics. Flip-up SIG iron sights are factory installed and ready for use, while the continuous top rail leaves ample room for optics.
A mid-length gas system softens recoil impulse, enhancing control during fast strings. Combined with the free-float handguard and quality barrel, the platform is tuned for accuracy and reliability straight from the box.