FN 509 NMS 9mm, BlackDescription 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. Over the course of development, the platform has been tested extensively for reliability, ammunition compatibility and durability totaling more than one million rounds.