This is a Ruger Single Six cylinder in .22lr. Factory Ruger part in a box with the red bag. The .22 mag cylinder apparently went with the gun and this was left undiscovered in a box. It has been used as is evident from the marks but is in overall good condition. Fluted cylinder with no external markings on it. Probably an early production version from what I've looked up on it. I haven't tried it in a firearm as I don't have a Single Six. Will ship on your dime.
