Frank Cannon's revolver...
In reality he probably had several, the television business being what it is and was.
The photo shown in this thread indicates a six shot revolver of some sort, but I remember a scene with our hero shooting at a distant target - camera stationed from his left side, slightly behind him - and the revolver in his outstretched hand clearly visible as a S&W Chief's Special.
As a further example of this, Deputy Barney Fife carried a six inch double action Colt revolver (a Police Positive, I think) in his duties. Except when it was a four inch Military & Police.
As an aside, the late William Conrad actually knew about firearms. He was a collector and shooter, probably laughing at himself making some of the shots one makes ONLY with a sympathetic writer. In fact, Mr. Conrad had a rather widespread field of interests and knowledge in reality.