The Sig Sauer M400 Sentry is an AR-pattern semi-automatic rifle chambered in 5.56 NATO (.223 Rem). It has a 16-inch barrel and ships as a package with a ROMEO 5 Gen II red dot sight and a Foxtrot MSR light. The magazine capacity is 30+1 rounds. 
 

Key Specifications 

• Brand: Sig Sauer 
• Model: M400 Sentry 
• Caliber: 5.56 NATO 
• Action: Semi Auto 
• Capacity: 30+1 
• Barrel Length: 16 in 
   

Detailed Features 

• AR-pattern semi-automatic rifle chambered in 5.56 NATO 
• 16-inch barrel 
• Package includes ROMEO 5 Gen II red dot sight 
• Package includes Foxtrot MSR light 
• 30-round magazine included

Owners of the M400 Sentry package appreciate getting a functional optic and light bundled with the rifle rather than assembling the kit separately. The ROMEO 5 Gen II is well-regarded for durability and clarity at its price tier, and the Foxtrot MSR light adds practical utility. The 5.56 NATO chambering keeps the platform compatible with common ammunition.

The M400 is Sig's AR-pattern gas-operated rifle, and most owners report solid reliability out of the box. The 16-inch barrel gives a balanced length for both field use and storage. The trigger feel on the base configuration draws some criticism for a heavier pull than aftermarket options, but it functions without issues.

The Sentry package is often compared to building a comparable setup from individual components. Most buyers find the bundled price reasonable when the sight and light are factored in. Owners who prefer a different optic sometimes see less value in the package, but for those who like the ROMEO 5 Gen II pairing, it represents a practical starting point.