CMMG Inc Magazine Extension Kit Five-seveN Pistol 10rd. 7mmX28mm 10 Round Mag Extention Black - 5.7 10 Round Mag Extension. The ultimate upgrade to your 5.7x28 pistol. Simply remove floor plate inspect factory mag opening for burrs (remove burrs as necessary) install extension insert spring and add floor plate. Installation takes only seconds and does not permanently alter factory magazine. Chrome silicon spring is salt water resistant and will not take a set. Specifications for CMMG Inc Magazine Extension Kit Five-seveN Pistol 10rd: Manufacturer: CMMG Gun Make: FN Herstal Gun Model: FN Five-seveN Caliber: 5.7x28mm Magazine Capacity: 10 Round Finish: Black Condition: New Package Contents: CMMG 57AFD1E FiveSeven 5.7mmX28mm 10 Round Mag Extention Black The CMMG 57AFD1E FiveSeven 5.7mmX28mm 10 Round Mag Extention Black is a quality addition to the CMMG lineup. For more great deals on Pistol Magazines by CMMG please browse our CMMG Inc Magazines page. What firearm models does the manufacturer say CMMG Inc Magazine Extension Kit Five-seveN Pistol 10rd is compatible with? The manufacturer says that CMMG Inc Magazine Extension Kit Five-seveN Pistol 10rd is compatible with FN Five-seveNCMMG 57AFD1E FiveSeven 5.7mmX28mm 10 Round Mag Extention Black