The FN 509M is a full-size 9mm DAO pistol chambered in 9MM Luger with a 4" barrel and 17+1 capacity. Its double-action-only trigger eliminates the need for external safeties, and the flat-face trigger face gives a consistent feel across different finger positions. 
 

Key Specifications 

• SKU: 2024020061 
• UPC: 845737018368 
• Brand: FN 
• Model Name: 509M 
• MPN: 66101930 
• Caliber: 9MM LUGER 
• Action: DAO (Double Action Only) 
• Capacity: 17+1 RD  
• Barrel Length: 4" 
• Overall Length: 7.40" 
• Weight: 1.65 lbs  
• Sights: Co-Witness Iron  
• Grip Type: Black Interchangeable Backstrap  
• Trigger Type: Flat Face  
• Safety Features: None (DAO configuration) 
• Finish: Matte Black  
• Condition: New in Box  
   

Detailed Features 

The DAO action keeps the trigger pull weight consistent from the first shot to the last, which some shooters find more predictable under stress than a DA/SA transition. There are no external safeties to disengage. 
 
Interchangeable backstraps let users adjust grip size to their hand. Co-witness iron sights align with most red-dot mounting heights. At 1.65 lbs, the pistol is on the lighter end for a full-size 17+1 platform. 
 

Target Audience 

The DAO configuration suits users who want a simple, consistent trigger for defensive or duty use. Competitive shooters who prefer striker-fired platforms may find the longer DA pull less ideal for speed work. 
 

Usage Scenarios 

• Home Defense: High capacity and DAO simplicity work well for a ready firearm. 
• Sport Shooting: Works for practice and casual competition; heavier trigger pull is a trade-off. 
• Everyday Carry: At 1.65 lbs unloaded, it is manageable for all-day carry with the right holster.

Feedback on the FN 509M Compact 9mm DAO Pistol tends to be positive on build quality and reliability, with some reservations around the trigger system.

Positive Aspects:

1. Ergonomics and Comfort: Most owners find the grip comfortable and the pistol easy to handle during range sessions.

2. Reliability: Commonly cited as a strength, owners report consistent function across various ammunition types.

3. Capacity: The 17+1 round count is frequently mentioned as a practical advantage over smaller-capacity options.

4. Build Quality: The construction earns praise for feeling solid and holding up to sustained use.

5. Sights and Accuracy: Factory sights are generally rated well for out-of-the-box accuracy.

Constructive Criticism:

1. Weight: Some users find it heavier than comparable compact options, which affects carry comfort.

2. DAO Trigger System: This is the most common point of debate. Owners who prefer shorter, lighter striker-fired pulls find the DAO less comfortable for fast shooting.

3. Price Point: A few buyers feel the price is high relative to alternatives with similar specs.

4. Accessory Compatibility: Some users want more aftermarket holster and sight options specifically tailored to this model.