The FN 509 Midsize is a striker-fired 9mm pistol built around a cold hammer-forged barrel, polymer frame, and matte black stainless slide. It runs without a manual safety, relying on a consistent DAO trigger pull of 5.5 to 7.5 pounds. 
 

Key Specifications 

• Brand: FN 
• Model: 509 Midsize 
• Caliber: 9MM Luger (9x19 Para) 
• Action: Striker Fired (DAO) 
• Capacity: 10+1 rounds 
• Barrel Length: 4 inches 
• Weight: 26.50 oz 
• Frame Material: Polymer with Matte Black Finish 
• Slide Description: Matte Black Stainless Steel 
• Safety Features: No manual safety 
• Sights Type: Fixed 3-Dot Luminescent 
   

Detailed Features 

The cold hammer-forged barrel improves durability and contributes to consistent shot-to-shot accuracy. Interchangeable backstraps let shooters fit the grip to their hand size, and the aggressive texture holds well under sweat or gloves. The three-dot luminescent sight system works in low light without requiring batteries or additional hardware. 
 

Usage Scenarios 

1. Home Defense: 10+1 capacity and controllable recoil make it a practical choice for defensive use. 
2. Sport Shooting: Consistent trigger and balanced weight support accurate work on the range. 
3. Everyday Carry: The midsize format conceals reasonably well for shooters who want a full-featured gun rather than a micro-compact.

The 509 Midsize draws praise for its ergonomics, accuracy, and build quality. The grip texture and interchangeable backstraps come up frequently as genuine functional advantages rather than marketing features. Shooters report tight groups at distance and consistent reliability across different ammunition brands.

The main criticisms are the trigger and the size. Some owners find the trigger pull heavier and less crisp than competing striker-fired pistols, though most rate it as an improvement over older FN designs. The midsize format is wide enough that it draws comment from shooters who prefer something thinner for concealed carry — it's not a subcompact. Aftermarket support is narrower than for Glock or SIG platforms, which is a real consideration for customizers.

Pricing sits above budget options, and a segment of potential buyers finds that harder to justify against comparably-specced competitors. Those who do buy generally report satisfaction with performance relative to cost.