MPA Mag Extender is designed for 308 Box magazines built by AICS or Accurate Mag â€“ single feed only. (Will not work with AW Mags). Simply remove the existing floorplate, remove the base insert (from the Accurate Mags only), depress the spring into the mag body, slide the mag extender in place and secure with the included 6-32 set screw. Make sure the mag spring has seated itself flush with the bottom of the mag extender. Produced from 6061 Aluminum. Cerakote Black Increases the magazine capacity to 14 rounds. These are for Accurate Mags.