The Sig Sauer M400 is an AR-pattern semi-automatic rifle chambered in 5.56 NATO. It has a 16-inch barrel and ships with a 30-round magazine. The stock is black synthetic with a telescoping design. 
 

Key Specifications 

• Brand: Sig Sauer 
• Model: M400 
• Caliber: 5.56 NATO 
• Action: Semi-Automatic 
• Capacity: 30+1 
• Barrel Length: 16 in 
• Color/Finish: Black 
   

Detailed Features 

• 16-inch barrel in a standard AR-pattern configuration 
• 30+1 round capacity with included magazine 
• Telescoping black synthetic stock 
• Semi-automatic operation on the AR platform 
• Synthetic furniture throughout

Owners of the Sig Sauer M400 tend to praise its out-of-the-box reliability and the fit and finish that Sig brings to the AR platform. The controls feel familiar to anyone who has run an AR-15, but the M400 gets credit for tighter tolerances than many budget-tier competitors.

Ergonomics get positive marks. The telescoping stock adjusts for different builds and shooting positions, and the 16-inch barrel keeps the rifle maneuverable without sacrificing much velocity. A few owners note the trigger is serviceable but not exceptional, and aftermarket upgrades are plentiful given the mil-spec architecture.

Value is where opinions split. Some see the M400 as a premium-priced option in a crowded market and feel the cost is justified by the Sig name and quality control. Others argue that the base configuration leaves room for improvement and that the money could go further with a self-built rifle.