The FN 509 MRD is a striker-fired 9mm pistol with a 4.5-inch barrel and Flat Dark Earth finish. It ships with a 10-round magazine and is set up for micro red dot mounting. 
 

Key Specifications 

• UPC: 845737011840 
• Action: Double Action (striker-fired) 
• Barrel Length: 4.5 inches 
• Caliber: 9MM Luger 9x19 Para 
• Capacity: 10 rounds 
• Finish: Flat Dark Earth 
• Weight: 1.75 lbs. 
   

Detailed Features 

The 4.5-inch barrel gives the 509 MRD a full-size feel and is long enough to extract good velocity from 9mm. The MRD designation refers to the factory-milled slide, which accepts micro red dots without a separate adapter plate. The double-action striker-fired trigger is consistent shot to shot. At 1.75 lbs empty, it's on the lighter end for a full-size 9mm. 
 
The Flat Dark Earth finish covers the polymer frame; the slide is typically black. 
 

Usage Scenarios 

• Home defense: 10-round capacity, optics-ready slide, and 4.5-inch barrel suit a defensive build well 
• Sport shooting: optics compatibility and consistent trigger support competition use 
• Duty or range use: the 509 platform is used by law enforcement and holds up to heavy round counts

The FN 509 MRD in FDE gets positive feedback on build quality and the factory optics-ready slide, which simplifies setting up a red dot without modification costs. Ergonomics are well-regarded. The grip texture is considered effective without being aggressive, and the controls are intuitive.

Accuracy with the 4.5-inch barrel is consistently rated well across different distances. Reliability is generally reported as solid.

The 10-round capacity is the most common point of friction for buyers in unrestricted states where higher-capacity magazines are available; in those cases some owners find it limiting compared to competitors. Weight comes up as a minor discussion point. Most find 1.75 lbs acceptable, but a few consider it heavier than preferred for daily carry.

Occasional reports of trigger or slide lock issues appear in reviews, though these read as outliers rather than a pattern. The FN 509 MRD holds its own in comparisons to other optics-ready 9mm pistols and is well-regarded for reliability and fit and finish.