The Sig Sauer M400 SDI is an AR-pattern semi-automatic rifle chambered in 5.56 NATO with a 16-inch threaded barrel. It has a Cerakote Flat Dark Earth finish and ships with a Magpul SL stock and a 30-round magazine. The 2-stage Matchlite Duo trigger is factory-installed. 
 

Key Specifications 

• Brand: Sig Sauer 
• Model: M400 SDI 
• Caliber: 5.56 NATO 
• Action: Semi Auto 
• Capacity: 30+1 
• Barrel Length: 16 in 
• Color/Finish: Flat Dark Earth (Cerakote) 
   

Detailed Features 

• 16-inch threaded barrel 
• Cerakote Flat Dark Earth finish on the receiver 
• Magpul SL stock 
• Factory-installed 2-stage Matchlite Duo trigger 
• 30-round magazine included

The M400 SDI attracts owners who want a factory AR with a quality trigger installed from the start. The 2-stage Matchlite Duo is the consistent highlight, with owners reporting a clean break and short reset that outperforms standard mil-spec triggers without any post-purchase work.

The Cerakote FDE finish holds up through field use, and the Magpul SL stock feels solid. Some owners note the SL has limited length-of-pull adjustment compared to fully adjustable aftermarket stocks, but most find the fit adequate for standard use.

Value opinions vary. Some see the trigger and finish package as a fair premium over a baseline M400; others note that building to the same spec costs less if you are comfortable doing parts work. The threaded barrel and standard AR compatibility are practical positives that come up regularly in owner discussions.