SIG SAUER M400 SDI-X Semi-Auto Rifle RM400SDI16BFDE — Description

The SIG SAUER M400 SDI-X RM400SDI16BFDE is a premium 5.56 NATO semi-automatic rifle built on SIG Sauer’s enhanced M400 SDI-X platform. Designed for shooters who demand upgraded ergonomics, modern features, and dependable performance, the SDI-X combines a proven direct-gas operating system with a fully ambidextrous lower receiver, Magpul SL stock, and a distinctive Flat Dark Earth (FDE) finish.

Featuring a 16-inch barrel, free-floating aluminum M-LOK handguard, and optics-ready upper receiver, the M400 SDI-X provides a versatile platform for range shooting, training, and general-purpose rifle applications. The rifle’s .223 Remington/5.56 NATO-compatible chambering offers ammunition flexibility while maintaining the reliability expected from SIG Sauer’s M400 series.

The SDI-X model upgrades the traditional AR-style layout with full ambidextrous controls, including left- and right-side controls for improved operation regardless of shooting preference. Combined with the adjustable Magpul SL stock and modular M-LOK handguard, the rifle offers a highly adaptable configuration with a premium factory setup.

SIG SAUER M400 SDI-X RM400SDI16BFDE — Specifications

Manufacturer: SIG SAUER
Model: M400 SDI-X
Model Number: RM400SDI16BFDE
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: Flat Dark Earth (FDE) 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 premium rifle configuration
• 5.56 NATO chambering
• 16-inch barrel
• Flat Dark Earth finish
• Magpul SL adjustable stock
• Fully ambidextrous lower receiver controls
• Ambidextrous safety selector and magazine release
• 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 upgrades

Package typically includes:

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