SKU CSSI|XI744114 Category

Sig Sauer M400 Black Rifle 5.56 NATO 30rd Magazine 16″ Barrel ROMEO-MSR GEN II Adjustable Stock M-LOK Handguard

Sig Sauer M400 Black Rifle 5.56 NATO 30rd Magazine 16″ Barrel ROMEO-MSR GEN II Adjustable Stock M-LOK Handguard

$999.99

20 in stock

Features:

  • TriggerTech 3.5 pound two-stage flat blade duty trigger
  • 16" cold hammer forged barrel with mid-length gas system
  • ROMEO-MSR Gen II 2 MOA red dot included
  • Full-length free-floating M-LOK handguard
  • Ambidextrous charging handle
  • MAGPUL SL-K 6-Position adjustable stock

Specifications:

  • FIREARM TYPE: Rifle
  • CALIBER: 5.56 NATO
  • SIGHTS: ROMEO-MSR GEN II w/2 MOA DOT
  • BARREL LENGTH: 16 in [406.4 mm]
  • BARREL MATERIAL: Cold Hammer Forged Steel
  • TWIST RATE: 1:7
  • THREADS: 1/2 in – 28 90 Degree Shouldered
  • MUZZLE DEVICE: A2 Birdcage Flash Hider
  • ACTION TYPE: Semi-Auto
  • OPERATING SYSTEM: Mid-Length Direct Impingement
  • STOCK TYPE: 6-Position Magpul SL-K
  • GRIP TYPE: Reduced Angle
  • TRIGGER TYPE: TriggerTech 3.5-Pound 2-Stage Flat Blade
  • TRIGGER SHAPE: Flat
  • MANUAL SAFETY: Ambidextrous
  • FOREND TYPE: M-LOK Black Cerakote
  • ACCESSORY RAIL: M-LOK/Full-Length Picatinny
  • MAG TYPE: AR-15
  • MAGS INCLUDED: (1) 30rd Polymer Mag
  • COLOR: Concrete Gray
  • RECEIVER FINISH: Black Cerakote
  • OVERALL LENGTH: 35.5 in [901.7 mm]
  • COLLAPSED LENGTH: 32.25 in
  • OVERALL WIDTH: 2.7 in [68.58 mm]
  • HEIGHT: 9.4 in [819.15 mm]
  • WEIGHT: 6.8 lb [3084.43 kg]

Additional information

Upc

798681744114

Manufacturer

Sig Sauer

Manufacturer part number

 RM400-556N-16B-FORGE

Action

Semi-Auto

Barrel length

16"

Capacity

30

Model

M400 Forge

Product type

AR

Rate of twist

1:7"

FAQ

BJ Firearms LLC is a federally licensed firearms business focused on providing quality firearms, accessories, and related services while promoting responsible ownership, education, and community engagement.

The company was founded to serve firearm enthusiasts with knowledgeable service, real-world experience, and a commitment to professionalism and safety.

We focus on real experience, personalized service, hands-on product knowledge, and community involvement — not just sales. Our goal is to help customers make informed decisions and feel confident with their equipment.

Yes. We operate as a federally licensed firearms dealer (FFL), following all applicable federal, state, and local regulations.

Yes. We partner with trusted suppliers to provide quality products and reliable sourcing.

Yes. We partner with content creators and industry professionals to provide real-world insights and experiences.

We work with everyone — from first-time buyers to experienced enthusiasts. Education and guidance are a big part of what we do.

We offer firearms, accessories, gear, and related equipment depending on availability and customer needs.

Yes. We help customers evaluate their needs, experience level, and intended use to find the right fit.

Yes. Depending on the request, we can help source specific products or assist with custom configurations.

Yes. We actively engage in hands-on experiences, demonstrations, and community-related firearm activities when possible.

Yes. We support content that helps people learn about equipment, safety, and responsible firearm ownership.

Social Media Posts

Via Vontaes_Gunz

Customer Reviews

“Outstanding customer service.” I had a lot of questions before buying, and they walked me through everything without pressure. Super knowledgeable and easy to work with. You can tell they actually care about their customers.
Verified Customer
“Best experience I’ve had buying gear.” Professional, responsive, and honest. They helped me choose exactly what I needed without overselling anything. I’ll definitely be coming back.
Verified Customer
“Great people, great service.” Very down-to-earth and easy to talk to. They explain things clearly and make sure you understand your options. Highly recommend, especially if you’re new.
Verified customer

BJ FIREARMS LLC

Age Verification Required.

You must be 18 or older to enter this website. By entering this website, you are agreeing to all policies and procedures.