Sig Sauer M400 SDI XSeries 5.56 NATO 16" 1:7" Bbl Black Rifle w/ Romeo5 Gen II Red Dot Sight, Foxtrot Rail Mtd Light & (1) 30rd

The Sig Sauer M400-Sentry SDI XSeries offers a turnkey solution for shooters seeking a high-performance 5.56 NATO rifle. This ready-to-go package includes a ROMEO5 GEN II red dot sight, FOXTROT-MSR™ Full-Size Rail-Mounted Light, and a vertical foregrip, all installed on the M400-SDI X platform—ensuring speed, precision, and superior low-light capability. Built around Sig’s mid-length direct impingement operating system, this AR-style rifle delivers outstanding reliability, a lightweight 16" barrel, and premium ergonomics.

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Key Features

• ROMEO5 GEN II Red Dot Sight

  • Rapid target acquisition with a 2 MOA dot.

  • Motion-activated illumination technology ensures extended battery life and instant-on activation.

• FOXTROT-MSR™ Full-Size Light

  • Optimized for tactical illumination in low-visibility conditions.

  • Rail-mounted for easy attachment/detachment and intuitive handling.

• 16" Chrome/Moly Steel Barrel

  • 1:7" twist rate ideal for stabilizing heavier 5.56 bullets.

  • 1/2 in - 28 tpi threads with SIG Flash Hider-Compensator for reduced muzzle rise.

• Mid-Length Gas System

  • Smoother recoil impulse for improved handling and faster follow-up shots.

  • Direct impingement ensures consistency and reliability.

• Ambidextrous Controls & 2-Stage MatchLite Duo Trigger

  • Enhanced fire control for precision and control.

  • Ambidextrous safety suitable for both right- and left-handed shooters.

• M-LOK Free-Floating Alloy Handguard

  • Provides superior rigidity and minimal barrel contact for maximum accuracy.

  • Equipped with Picatinny rail sections to mount optics, lights, and foregrips.

• Complete Accessories

  • Vertical Foregrip for enhanced weapon control and maneuverability.

  • 6-Position Magpul MOE-SL Stock for easy length-of-pull adjustments.

  • Reduced Angle Grip for improved ergonomics.

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Specifications

• Model: RM400-SDI-16B-R5FX

• Caliber: 5.56 NATO

• Barrel Length: 16 in (406.4 mm)

• Barrel Material: Chrome/Moly Steel

• Twist Rate: 1:7

• Thread Pitch: 1/2 in - 28 tpi (tapered shoulder)

• Muzzle Device: SIG Flash Hider-Compensator

• Operating System: Mid-Length Direct Impingement

• Trigger: SIG 2-Stage Matchlite Duo (Flat)

• Stock/Brace: 6-Position Magpul MOE-SL (Black)

• Handguard: Free-Floating M-LOK Alloy (includes FOXTROT-MSR Light & Vertical Foregrip)

• Grip: Reduced Angle

• Sights: ROMEO5 GEN II Red Dot (installed)

• Magazine Included: One (1) 30-round Polymer Mag

• Weight (Approx.): 8.0 lb

• Overall Length: 36.5 in (extended) / 33.25 in (collapsed)

• Finish: Black Anodized

• Forward Assist: Yes

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Why Choose the Sig Sauer M400-Sentry SDI XSeries?

• Complete Package – Includes red dot, rail-mounted light, and foregrip for instant readiness.

• Mid-Length Gas System – Reduces recoil, boosts handling, and extends component life.

• Precision & Reliability – SIG’s build quality and 2-Stage MatchLite Duo Trigger ensure accurate, consistent shots.

• Ambidextrous Controls – Accommodates right- or left-handed operation, improving ease of use.

• Trusted Sig Sauer Engineering – A name synonymous with duty-grade performance and unmatched craftsmanship.