My aunt has an old Model 13-4. Appears to be a 4" Heavy Barrel. Has a round butt with serrations on the grip frame. I expect it is possibly my uncle's old service revolver, but not sure. I know he was in the Secret Service for a time, and was Capitol Police after that. I would guess that he retired sometime in the late 90's/Early 2000's, but not sure. Unfortunately he is no longer around and she is not really able to answer questions about it. I was wondering if either of these agencies might have issued a M13-4 with a round butt and 4" HB?

Thank you.