It is an early Combat Magnum, now known as the Model 19.
If it does not have the model number on the frame inside the yoke, it was made between 1955 when the Combat Magnum was introduced and 1957 when model numbers were adopted.
If it has the model number inside the yoke it was made between 1957 when model numbers were assigned and 1961 when they dropped the cylinder stop screw from in front of the trigger guard.
The wider target hammer, target trigger and target stocks were optional at extra cost. If the grips are numbered to the gun, it adds a good deal to the value. (I have one similar but I had to find and add the target stocks, fortunately before their value took off.)
Maybe an expert will come along who can tell you more. The serial number will let him pin down the year made.