SIG SAUER M400 Sentry Package Semi-Auto Rifle RM400SDI16BR5FX — Description

The SIG SAUER M400 Sentry Package RM400SDI16BR5FX is a complete 5.56 NATO semi-automatic rifle package built on SIG Sauer’s proven M400 platform. Designed as a ready-to-use defensive, sporting, and training rifle, the Sentry Package combines a reliable direct-impingement operating system with factory-installed accessories including a ROMEO5 red dot sight, FOXTROT-MSR weapon light, and a 6-position stock.

The M400 Sentry features a 16-inch barrel, lightweight aluminum receivers, a free-floating M-LOK handguard, and SIG Sauer’s 2-stage Matchlite Duo trigger for improved trigger control. The included ROMEO5 optic provides a fast-acquisition aiming solution, while the FOXTROT-MSR light adds a high-output illumination option for low-light applications.

Built around the AR-15 pattern platform, the rifle offers familiar controls, standard magazine compatibility, and a modular design that allows users to customize the rifle with additional optics, grips, slings, and accessories. The package includes a 30-round magazine, making it a complete setup straight from the factory.

SIG SAUER M400 Sentry Package RM400SDI16BR5FX — Specifications

Manufacturer: SIG SAUER
Model: M400 Sentry Package
Model Number: RM400SDI16BR5FX
Caliber: 5.56 NATO (.223 Remington compatible)
Action: Semi-automatic
Operating System: Direct impingement gas system
Platform: AR-15 style rifle

Barrel Length: 16 inches
Barrel Material: Carbon steel
Barrel Twist Rate: 1:7″
Receiver Material: Aluminum
Finish: Black anodized finish
Stock: 6-position adjustable SL stock
Handguard: Free-floating M-LOK handguard
Trigger: SIG 2-stage Matchlite Duo trigger
Magazine Type: AR-15 / STANAG compatible detachable magazine
Magazine Capacity: 30 rounds
Muzzle Device: Flash hider, 1/2×28 thread pitch
Sights/Optics: SIG ROMEO5 red dot sight included
Weapon Light: SIG FOXTROT-MSR rifle light included
Overall Length: Approx. 36.5 inches
Weight: Approx. 8 lbs (with accessories)

Included Accessories

SIG ROMEO5 Red Dot Sight

• 1x magnification
• 2 MOA red dot reticle
• Motion-activated illumination system
• Multiple brightness settings
• Designed for carbine and MSR platforms

SIG FOXTROT-MSR Rifle Light

• High-output white light system
• 1,350 lumens
• 33,000 candela
• Includes mounting options for M-LOK and Picatinny rails
• Remote tape switch capability

Key Features

• Complete factory rifle package
• 5.56 NATO chambering
• 16-inch barrel for balanced performance
• SIG 2-stage Matchlite Duo trigger
• Free-floating M-LOK handguard
• ROMEO5 red dot optic included
• FOXTROT-MSR weapon light included
• 6-position adjustable stock
• AR-15 magazine compatibility
• 30-round magazine included
• Optics-ready and accessory-ready platform
• SIG Sauer M400 reliability and modularity

Package typically includes:

• SIG SAUER M400 Sentry 5.56 NATO rifle
• SIG ROMEO5 red dot sight
• SIG FOXTROT-MSR rifle light
• 6-position adjustable stock
• 30-round magazine
• Owner’s manual and safety documentation