SIG SAUER M400 SDI-X Semi-Auto Rifle RM400SDI16BMSGRN — Description

The SIG SAUER M400 SDI-X RM400SDI16BMSGRN is a premium 5.56 NATO semi-automatic rifle built on SIG Sauer’s enhanced M400 SDI-X platform. Designed for shooters seeking upgraded performance and ergonomics, the SDI-X combines a lightweight direct-gas operating system with fully ambidextrous controls, a free-floating M-LOK handguard, and premium SIG Sauer components.

Featuring a 16-inch barrel, Moss Green (OD Green) finish, and Magpul SL stock, the M400 SDI-X offers a modern AR-platform configuration with improved handling and adaptability. The rifle uses a mid-length gas system, rotating bolt design, and a 30-round magazine configuration for a versatile setup suitable for range shooting, training, and general-purpose use.

The SDI-X model upgrades the standard M400 design with a fully ambidextrous lower receiver, including controls optimized for left- or right-handed operation. Its free-floating aluminum M-LOK handguard provides accessory mounting flexibility while maintaining a lightweight profile.

SIG SAUER M400 SDI-X RM400SDI16BMSGRN — Specifications

Manufacturer: SIG SAUER
Model: M400 SDI-X
Model Number: RM400SDI16BMSGRN
Caliber: 5.56 NATO (.223 Remington compatible)
Action: Semi-automatic
Operating System: Direct gas impingement with rotating bolt
Platform: AR-15 style rifle

Barrel Length: 16 inches
Barrel Twist Rate: 1:8″
Barrel Type: SIG precision barrel
Gas System: Mid-length gas system
Receiver Material: Aluminum
Finish: Moss Green / OD Green finish
Handguard: Free-floating aluminum M-LOK handguard
Stock: Magpul SL adjustable stock
Magazine Type: AR-15 / STANAG compatible magazine
Magazine Capacity: 30 rounds
Trigger: SIG factory enhanced trigger system
Controls: Fully ambidextrous controls
Rail System: Full-length Picatinny top rail
Muzzle Thread: 1/2×28 TPI
Overall Length: Approx. 32–35 inches (stock position dependent)
Weight: Approx. 7 lbs (configuration dependent)

Key Features

• M400 SDI-X enhanced rifle configuration
• 5.56 NATO chambering
• 16-inch barrel
• Moss Green / OD Green finish
• Magpul SL adjustable stock
• Fully ambidextrous lower receiver controls
• Ambidextrous magazine release and safety selector
• Free-floating M-LOK handguard
• Mid-length gas system
• 1:8 twist barrel for ammunition versatility
• Lightweight aluminum receiver construction
• AR-15 magazine compatibility
• 30-round magazine included
• Optics-ready Picatinny rail
• SIG Sauer SDI-series performance upgrades

Package typically includes:

• SIG SAUER M400 SDI-X rifle
• 30-round magazine
• Magpul SL stock
• M-LOK handguard system
• Owner’s manual and safety documentation