The FN 509 is a full-size 9mm Luger striker-fired pistol with a 4-inch barrel, 17+1 capacity, and double-action-only operation. Overall length is 7.4 inches, weight is 26.9 oz (1.68 lbs). The Flat Dark Earth polymer frame pairs with an FDE steel slide. Two magazines are included. Sights are fixed 3-dot luminescent. Interchangeable backstraps allow grip customization. 
 

Key Specifications 

• Brand: FN 
• Model: 509 
• Caliber: 9mm Luger 
• Action: Striker Fired (Double Action Only) 
• Barrel Length: 4 inches 
• Overall Length: 7.4 inches 
• Weight: 26.9 oz (1.68 lbs) 
• Capacity: 17+1 rounds 
• Magazines Included: 2 
• Frame Material: Polymer with Flat Dark Earth finish 
• Sights Configuration: Fixed 3-Dot Luminescent sights 
   

Detailed Features 

 
The striker-fired mechanism delivers a consistent trigger pull across every round. Interchangeable backstraps let you set grip size before you shoot rather than working around a fixed frame. The FDE frame and steel slide are well-matched and hold up to regular use. At 17+1 rounds, the capacity suits both defensive and competitive applications without requiring frequent mag changes. Luminescent fixed sights acquire targets quickly in reduced-light conditions. 
 

Target Audience 

 
New shooters who want a full-size 9mm from a trusted manufacturer. Experienced owners looking for a reliable range or home defense pistol. Competitive and recreational shooters who want high capacity in an FN platform. 
 

Usage Scenarios 

 
Home defense and range work are the main applications. The 17+1 capacity is well-suited to defensive scenarios where round count matters. The consistent trigger pull and luminescent sights work well in competitive shooting. The interchangeable backstraps make it adaptable to different shooters during training sessions.

The FN 509 FDE generates consistent appreciation for reliability and ergonomics, with aftermarket support and trigger feel as the recurring critiques.

Build quality and FN's track record are the first things most owners mention. The 509 is described as solid and dependable, which is what most buyers expect from the brand. The grip and ergonomic design are praised for comfort during extended sessions. Luminescent sights get specific credit for low-light visibility, adding useful versatility. The 17+1 capacity is viewed as a genuine advantage for both defensive and recreational use.

Aftermarket accessory availability is the main criticism. Compared to Glock or Sig Sauer, the FN 509 has a smaller ecosystem of compatible parts and accessories, which limits customization. The trigger generates some debate: many users describe it as crisp and usable, but others want a more refined feel. This is worth evaluating in person if trigger preference is a priority.

The overall picture is a reliable, well-built full-size 9mm with a competitive capacity and some trade-offs in customization and trigger refinement.