FCW carbon fiber mag extension for the Tristar Viper G2 Viper Max and Cobra II by Armsan 12ga shotgun. Adds 5 rounds of 2-3/4� shells. Adds approx. 12 in length and 4.10 oz in weight. Comes with our SS extreme duty spring and wrench. The FCW aluminum support clamp is recommended for use with this extension and can be purchased separately.