Yes, it's possible the cylinder is a replacement, if you are sure there's no serial number on it. Check the grip frame straps under the grips for evidence of any factory rework stamps. If the factory replaced the cylinder, there will be a date code stamped on the left strap. Any service dep't work done would be indicated by a small parallelogram stamp, or an "S' stamp, depending on the era the work was done. If you can post the full serial number, I may be able to tell you when the gun was made. Ed.