The Sig Sauer M400 Forge is a semi-automatic AR-pattern rifle chambered in 5.56 NATO with a 16-inch barrel and 30-round capacity. The alloy receiver is finished in Concrete Gray Cerakote and the handguard is M-Lok. It ships with a Magpul SL-K stock, black polymer grip, and the Sig ROMEO-MSR Gen II optic. 
 

Key Specifications 

• Brand: Sig Sauer 
• Model: M400 Forge 
• Caliber: 5.56 NATO 
• Action: Semi Auto 
• Capacity: 30rd 
• Barrel Length: 16in 
• Color/Finish: Concrete Gray Cerakote 
   

Detailed Features 

• 16-inch barrel on an alloy receiver with Concrete Gray Cerakote finish 
• M-Lok handguard with Picatinny rail on top 
• Magpul SL-K black polymer stock 
• Black polymer grip 
• Includes Sig ROMEO-MSR Gen II red dot optic

Owners of the M400 Forge cite the Concrete Gray Cerakote finish as a practical choice that resists holster wear and gives the rifle a distinctive look without standing out. The M-Lok handguard layout gets consistent praise for allowing clean accessory placement without extra adapters.

The included ROMEO-MSR Gen II optic draws mixed reactions. Buyers who wanted a ready-to-shoot package see it as a value add, but experienced shooters who already have a preferred optic sometimes find the bundled red dot redundant. The Magpul SL-K stock is regarded as functional, and its adjustable length-of-pull covers a wide range of users, though a small number find the cheek weld lower than expected for optic use.

At its price tier, the M400 Forge is generally considered competitive with other optic-included AR packages. The common complaint is that the build quality, while solid, does not clearly exceed AR-pattern rifles in the same range that come without an optic. Reliability over standard 5.56 NATO ammunition is rarely questioned by owners.