The Ferret50 upper receiver manufactured by Spider Firearms is designed as a modular system which can convert an AR-15 style lower receiver into a single shot bolt action rifle chambered for .50 BMG. Features a three-lug bolt, claw type extractor, plunger type ejector, free-floating Lothar Walther Supermatch heavy stainless steel barrel with four-chamber muzzle brake capable of .2MOA accuracy, and a detachable bipod. The upper is fitted to a standard CMMG Inc. Model 4SA lower receiver with target style pistol grip and solid buttstock. Includes a Leupold Osprey 10-40x50 scope.