SIG SAUER M400 5.56 NATO 16-Inch Rifle with ROMEO5

The SIG SAUER M400 5.56 NATO 16-Inch ROMEO5 configuration is the current M400-TREAD V2 COIL, an AR-15-pattern semi-automatic rifle chambered in 5.56x45mm NATO.

SIG identifies the rifle as RM400-16B-TRD-V2-COIL. The package combines the updated TREAD V2 rifle with a factory-installed ROMEO5 GEN II red-dot sight, vertical foregrip and barricade stop.

SIG SAUER M400 5.56 NATO ROMEO5 Overview

The M400-TREAD V2 COIL builds on SIG’s current TREAD V2 architecture with a free-floating enhanced M-LOK handguard, mid-length gas system and six-position Magpul SL-K stock.

The aluminum receiver uses a black anodized finish, while the rifle retains familiar AR-15 controls and magazine compatibility. SIG also equips this configuration with an ambidextrous safety and magazine release.

For additional firearm specifications and model references, browse the Gunvexa firearm reference catalog.

M400 5.56 NATO Chambering

The rifle is chambered in 5.56 NATO and uses standard AR-15-pattern magazines.

The current factory package includes one 30-round polymer magazine. The rifle’s AR-based receiver architecture uses a rotating bolt with direct-impingement operation.

16-Inch Stainless-Steel Barrel

SIG specifies a 16-inch stainless-steel barrel with a 1:8 twist rate.

The muzzle uses a 1/2×28 tapered-shoulder thread configuration and is fitted with a SIG three-prong flash hider.

Gas operation is mid-length direct impingement, distinguishing the M400 from SIG’s piston-operated MCX rifle family.

ROMEO5 GEN II Red Dot

A defining feature of the COIL package is the factory-installed ROMEO5 GEN II.

The optic provides 1x magnification through a 20mm aperture and uses a compact red-dot format. SIG’s current ROMEO5 GEN II specification includes MOTAC motion activation, a CR2032 battery, 12 illumination settings and an IPX7-rated housing.

Because the optic is factory included, it should remain part of the Gunvexa product title and short description for this specific package.

Matchlite Trigger, M-LOK Handguard and Stock

The M400-TREAD V2 COIL uses SIG’s 2-Stage Matchlite Duo flat trigger.

Around the barrel is SIG’s enhanced free-floating black alloy M-LOK handguard. The factory package additionally includes an M-LOK vertical foregrip and barricade stop.

At the rear, the rifle uses a six-position Magpul SL-K telescoping stock and a reduced-angle pistol grip.

For official technical information, see the SIG M400-TREAD V2 COIL product page.

SIG SAUER M400 Technical Summary

Overall, the SIG SAUER M400 5.56 NATO 16-Inch ROMEO5 package combines a 16-inch stainless barrel, 1:8 twist, mid-length direct-impingement system and enhanced M-LOK handguard with factory-installed accessories.

The Matchlite Duo trigger, Magpul SL-K stock, ambidextrous controls and ROMEO5 GEN II distinguish the RM400-16B-TRD-V2-COIL package from the basic TREAD V2 rifle.

M400 TREAD V2 COIL Key Specifications

• Manufacturer: SIG SAUER
• Model: M400-TREAD V2 COIL
• Series: SIG M400
• SKU / MPN: RM400-16B-TRD-V2-COIL
• Commercial UPC: 798681726202
• Firearm type: Rifle
• Platform: AR-15 pattern
• Action: Semi-automatic
• Caliber: 5.56 NATO
• Operating system: Mid-length direct impingement
• Bolt system: Rotating bolt
• Barrel length: 16 inches
• Barrel material: Stainless steel
• Twist rate: 1:8
• Muzzle thread: 1/2×28 tapered shoulder
• Muzzle device: SIG three-prong flash hider
• Handguard: TREAD Enhanced
• Handguard material: Alloy
• Handguard type: Free floating
• Accessory interface: M-LOK
• Trigger: SIG 2-Stage Matchlite Duo
• Trigger shape: Flat
• Stock: Magpul SL-K
• Stock positions: Six
• Grip: Reduced angle
• Safety: Ambidextrous
• Magazine release: Ambidextrous
• Magazine pattern: AR-15
• Magazine capacity: 30 rounds
• Magazines included: One polymer magazine
• Optic: ROMEO5 GEN II
• Optic type: Red dot
• Optic magnification: 1x
• Optic aperture: 20mm
• Optic battery: CR2032
• Optic technology: MOTAC
• Optic illumination settings: 12
• Receiver finish: Black anodized
• Color: Black
• Vertical foregrip: Included
• Barricade stop: Included
• Forward assist: Yes
• Published weight: Approximately 7 lb
• Published collapsed length: Approximately 32.5 inches