Fin Stabilized: Self-Rifling Provides Superior Range And Accuracy Brittle Polystyrene Shell: Allows Breakages On Targets At Extended Range. Withstands Extreme Temperatures, Moisture And Humidity. Photodegradable And Environmentally Friendly .68 Caliber: Compliant With ASTM Safety Requirements Ultra Thick Fill: Superior Marking And Visibility Barrel bore size of .687-.690 is recommended