A mold and molding method for all plastic shotshell cases to inject the plastic into the mold cavity from a sprue at the center of the mold cavity forming the closed end of the shotshell case and to simultaneously fill all portions of the mold cavity without necessitating forming a weld line, and maintaining the entire periphery of the shotshell case uniform in thickness by holding the core within the mold cavity concentrically of the movable mold parts with a rigid core pin on the end of the core and seated in the sprue, the core pin having grooves for carrying molten plastic into the cavity while the pin is seated in the sprue for holding the core concentric of the mold cavity.