Sig Sauer M400 SDI SENTRY | 5.56 NATO | 16″ | RM400-SDI-16B-R5FX

The Sig Sauer M400 SDI SENTRY is a complete AR-platform rifle package built on the M400-SDI X chassis. It ships equipped with a ROMEO5 Gen II red dot, a Foxtrot-MSR full-size weapon light, a vertical foregrip, and a 30-round polymer magazine for an out-of-the-box field-ready configuration. This model uses a 16″ chrome-moly barrel and a mid-length operating system for balanced handling and reliable function. For users who prefer a magnified low-power variable, the Vortex Strike Eagle 1-6×24 pairs well with this rifle and is commonly available for under $1,000.

Applications: recreational target shooting and advanced training with an emphasis on modular accessory use and low-light capability provided by the integrated Foxtrot-MSR light.

Product Specifications

• The UPC is 798681716128.
• The manufacturer is Sig Sauer.
• The model is listed as M400 with the SENTRY combo configuration.
• The manufacturer’s part number is RM400-SDI-16B-R5FX.
• The cartridge is .223 REM/5.56 NATO.
• The barrel length is 16″.
• The barrel material is Chrome / Moly Steel.
• The twist rate is 1:7 (1-in-7″ rate of twist).
• The magazine capacity is 30 rounds and it includes one 30-round polymer magazine.
• The muzzle device is a Flash Hider (SIG flash hider-compensator noted).
• An optic is installed: ROMEO5 GENII red dot.
• A weapon light is installed: Foxtrot-MSR Full Size light.
• The stock is a 6-Position Magpul MOE-SL in black.
• The listed weight is 8.0 lb.
• The overall length is 36.5 in with a collapsed length of 33.25 in.

This M400 SENTRY package is configured to deliver a versatile, user-friendly AR experience with factory-installed sighting, illumination, and an ergonomic foregrip. The combination of a proven direct-impingement operating system, a 16″ chrome-moly barrel with a 1:7 twist, and a 2-stage Matchlite trigger gives shooters a reliable platform for precision-oriented practice and organized training. The included ROMEO5 Gen II and Foxtrot-MSR light expand the rifle’s utility in variable lighting, while the Magpul MOE-SL stock provides adjustable ergonomics for most shooters. Whether used for range-focused target work or instructor-led skill development, the M400 SENTRY presents a straightforward, accessory-ready option for informed shooters seeking a complete AR package.

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