The FN 509 is a 9mm striker-fired pistol with a 4-inch cold hammer-forged barrel, 17-round capacity, matte black finish, and a lightweight polymer frame. It weighs 1.7 lbs. 
 

Key Specifications 

• Caliber: 9MM Luger (9x19 Para) 
• Action: Striker Fire 
• Capacity: 17 Rounds 
• Barrel Length: 4 inches 
• Weight: 1.7 lbs 
• Sights: 3-Dot Fixed 
• Finish: Matte Black 
   

Detailed Features 

 
FN's cold hammer-forging process produces a barrel with tighter tolerances and longer service life than button-rifled alternatives. The polymer frame keeps weight at 1.7 lbs. Interchangeable backstraps accommodate different hand sizes. The textured grip surface holds securely under recoil. 
 
Three-dot fixed sights provide a straightforward aiming reference. The 17-round capacity matches most full-size 9mm service pistols. 
 

Usage Scenarios 

 
The FN 509 suits personal defense, duty carry, and range training. The full-size frame and 17-round capacity make it less suited for concealed carry compared to compact variants, but it handles well for holster carry and range work.

Reliability is the FN 509's consistent strong point. Owners report smooth function across various 9mm ammunition types, and the cold hammer-forged barrel's durability over high round counts is frequently cited. The ergonomics are well-received -- the grip texture provides confidence during shooting and the 17-round capacity gives good magazine endurance.

The 3-dot sights work fine for most users, though shooters accustomed to suppressor-height or competition sights sometimes upgrade them. Trigger feedback is the most common critique: factory pull weight is adequate but some owners describe it as heavier or less refined than aftermarket alternatives, which leads to trigger upgrades.

Size is a consideration. At full-size dimensions the 509 isn't optimized for concealed carry, and some users note this when comparing it to the 509 Compact or other mid-size options. Overall, owners characterize it as a dependable and capable service pistol that performs consistently without demanding much maintenance attention.