The FN Model 509 has became an offshoot of the earlier United States Army Modular Handgun System, developed to succeed the aging Italian Beretta M9 - the ultimate winner becoming the SIG-Sauer P320. The Model 509 is a modified form of the competition entrant, revised for civilian, security, and law enforcement market sales and use.
The gun uses a standard polymer / cold hammer-forged stainless steel combination frame design with full-length, ribbed slide assembly. Accessories can be mounted on a short section of MIL-STD-1913 rail under the muzzle and ahead of the trigger unit. No manual safety is present. Passive safeties are part of the base design. A 10-round magazine is offered to adhere to state regulations though the standard feed is a 17-round capacity form. The barrel, measuring 4" in length, can be threaded to accept a suppressor. A loaded chamber indicator showcases to the operator the status of the firing chamber. The trigger is Double-Action Only (DAO) and iron combat-style sights are of the fixed, three-dot luminescent style (law enforcement receives access to a fixed 3-dot night sight version). Backstraps are interchangeable. Overall length of the weapon reaches 7.4 inches. The slide stop lever and magazine release are ambidextrous.
Current market forms are the FN 509 and FN 509 tactical, the latter with threaded barrel, Low-Profile Optics Mounting System (LPOMS) and optional 24-count extended magazine.