Maxim Defense built the MDX 516 as a semi-automatic AR-pattern rifle chambered in 5.56 NATO / .223 Remington, with a 16-inch barrel and an MLOK handguard for accessory mounting. It carries a black Cerakote finish for added durability and is set up to run a standard 30-round AR magazine, giving it a configuration built around accessory flexibility and a clean, tactical look. 
 

Key Specifications 

• Brand: Maxim Defense 
• Model: MDX 516 
• Caliber: 5.56 NATO 
• Action: Semi Auto 
• Barrel Length: 16 inches 
• Finish: Black Cerakote 
   

Detailed Features 

• 16-inch barrel keeps the rifle balanced for both close range handling and mid-range use 
• MLOK handguard accepts standard MLOK accessories, including lights, grips, and rail sections, without extra adapters 
• Black Cerakote finish adds wear and corrosion resistance over a plain anodized finish 
• Ships set up to run a standard 30-round AR magazine 
• 5.56 NATO / .223 Remington chambering keeps the rifle compatible with widely available ammunition and standard AR-pattern magazines

AR-pattern rifles in 5.56 have decades of parts and design refinement behind them, and the MDX 516 benefits from that established platform. Owners generally expect an AR in this caliber to run reliably once it is broken in, and Maxim Defense's reputation in the AR space, built largely on its buffer systems, gives some buyers extra confidence in the rest of the build.

A 16-inch barrel is a common middle ground for AR owners who want a rifle that handles well both indoors and at longer range. The MLOK handguard is popular because it lets owners mount lights, grips, and slings without extra tools or adapters, and most describe swapping accessories on it as straightforward.

The AR platform has about the deepest aftermarket support of any rifle family, so MDX 516 owners can find replacement parts, optics mounts, and furniture from dozens of makers. Some buyers note that a black Cerakote finish costs more than a standard anodized rifle, but most consider the added durability worth it for a rifle used regularly.