The FN 509 is built on the proven architecture of the FNS Compact, FN made changes internally and externally to meet the rigorous performance standards of the MHS requirements and further developed the platform into the FN 509 with the help from industry experts. This model features 4" cold hammer-forged stainless steel barrel, combat-style sights, and improved front and rear cocking serrations. It also features a MIL-STD 1913 accessory mounting rail, and interchangeable backstraps. It has a double action operation, fully ambidextrous slide stop lever and magazine release, as well as fixed 3 dot luminescent sights. This model also features a polymer construction with replaceable steel frame/slide rails.