MagPump Magazine Retainer 9mm Double Stack Magazines FN 509 Black. The pump-action double mag return spring on this Speed Loader from MagPump is durable and uniquely designed for double stack magazines. The MagPump FN 509 9mm Double Stack Magazine Retainer Refreshes and adapts your existing magazines to work with the new magazine return spring technology. The factory mag spring retainers on your FN 509 magazines have been discontinued. With these MagPump FN 509 9mm - Double Stack Magazine Refreshers you can get a pump action magazine loader for your Glock SIG Smith & Wesson CZ or Ruger magazines. Specifications for MagPump FN 509 9mm Double Stack Magazine Retainer: Manufacturer: MagPump Caliber: 9mm Luger Gun Make: FN Herstal Gun Model: FN 509 Country of Origin: USA Package Contents: MagPump FN 509 9mm Double Stack Magazine Retainer MagPump MR-FN509: Magazine Retainer 9mm Double Stack Magazines FN 509 Black