The Maxim Defense MDX-516 is a semi-automatic AR-pattern rifle chambered in 5.56x45mm (.223 Remington) with a 16-inch barrel finished in URB Gray. It accepts 30-round magazines and is built around the MDX platform with the URB Gray color scheme applied throughout. 
 

Key Specifications 

• Brand: Maxim Defense 
• Model: MDX-516 
• Caliber: 5.56x45mm / .223 Remington 
• Action: Semi Auto 
• Barrel Length: 16 in 
• Color/Finish: URB Gray 
• Capacity: 30 
   

Detailed Features 

• 16-inch barrel in semi-automatic AR-pattern configuration 
• Chambered for both .223 Remington and 5.56x45mm 
• URB Gray finish applied to the exterior 
• 30-round magazine capacity 
• MDX-516 platform with Maxim Defense proprietary geometry

Owners of the Maxim Defense MDX-516 often mention the URB Gray finish as a differentiator, with most finding it holds up well over time. The MDX platform generates strong interest from buyers who want a departure from standard AR aesthetics without sacrificing parts compatibility.

Shooters who have run the MDX-516 at the range report it handles 5.56x45mm reliably across ammunition types, and the 16-inch barrel offers good general-purpose performance. A recurring complaint is that Maxim Defense pricing sits above competitors offering similar specifications, which some owners feel is only partially offset by the finish quality and brand cachet.

Aftermarket support is a mixed topic. The MDX-516 shares enough with standard AR geometry that most common accessories fit, but some Maxim-specific components require going directly through the manufacturer, which can frustrate owners looking for quicker solutions at local shops.