The Umarex 17rds GLOCK 17 Gen4 Co2 spare airsoft magazine by KWC is made from heavyweight aluminum, giving a hefty feel to the G17 GEN4 FULL BLOWBACK Airsoft pistol. This Co2 Umarex magazine has a high-efficiency internal gas system providing excellent FPS output, and reinforced valves and seals for optimal gas retention. Please note this ONLY for the KWC Glock 17 Gen4 FULL BLOWBACK Version, WILL NOT fit VFC Glock Series