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The OSS stinger pen pistol and several other clandestine pen guns, as well as homemade zip guns often made using plumbing parts, and cane guns used for both defense and poaching use a screw thread to attach the chambered barrel to a receiver with some sort of breech and firing pin. The user unscrews the barrel from the receiver to expose the chamber to load a cartridge. The RN50 .50 BMG single-shot rifle uses a similar screwthread breech cap to allow an otherwise simple break-action to contain a .50 BMG cartridge[citation needed].