The First Strike T15 Barrel Adapter - Auto Cocker allows for the use of after market barrel systems with the Tiberius Arms T15. The Tiberius Arms T15 Barrel Adapter is a one piece unit providing a T15 rear design for mounting to your marker and a standard thread type for an aftermarket barrel. Take advantage of the ability to rotate between hopper and magazine fed options while using your favorite after market barrel with the Tiberius Arms T15 Barrel Adapter!