Franklin Armory F17-X Complete Upper Receiver, 10-round configuration. Comes with everything needed to install on a Milspec AR complete lower receiver. Chambered in .17 Winchester Super Magnum, this piston-driven upper provides a cleaner, flatter shooting solution for pest control. The F17-X R2 uses a new Osprey Defense slim piston system that automatically adjusts for suppressed or unsuppressed use and works with most suppressors.