Sig Sauer M400 SDI Sentry 5.56 NATO 16in ROMEO5 Combo

About this product

The Sig Sauer M400 SDI Sentry is a factory-equipped AR-platform rifle supplied as a complete combo for immediate use. It pairs the M400-SDI X chassis with a ROMEO5 Gen II red dot and a Foxtrot-MSR full-size weapon light, mounted on a free-floating M-LOK handguard that includes a vertical foregrip. Factory features include ambidextrous controls, a 6-position Magpul MOE-SL stock, and a 16-inch chrome moly barrel with a 1:7 twist suitable for standard 5.56 NATO/.223 Remington ammunition. The package includes one 30-round polymer magazine and a threaded muzzle with a SIG flash hider-compensator.

Key Specifications

• The caliber is 5.56 NATO (.223 Rem).
• The barrel measures 16 inches.
• The rifling twist rate is 1:7.
• The barrel material is Chrome Moly Steel.
• An optic is installed: ROMEO5 Gen II red dot (installed).
• The weapon light is a Foxtrot-MSR full-size light (1250 lumens).
• Included magazine: One 30‑round polymer magazine.
• The stock is a 6-position Magpul MOE-SL.
• The unloaded weight is 8.0 lb.
• The muzzle is fitted with a 1/2×28 threaded SIG flash hider-compensator.

Built to SIG Sauer’s standards, the M400 SDI Sentry combo delivers a practical, modular platform for range use, training, or personal preparedness. Its factory-installed sight and light package, ambidextrous controls and M-LOK interface provide immediate functionality and simple upgrade paths for users who value straightforward ergonomics and dependable operation. The combo format means a shooter can take the rifle from box to the firing line with minimal setup while retaining flexibility for accessories and configuration changes down the road.

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