Assuming it is stainless and not a refinish, the gun is probably a Model 66 that was mis-stamped 19-3. I have heard of this happening before and incorrect stampings of model number by S&W are well documented.

In addition, if the parts are stainless, there should be an S stamped in the ejector rod shroud and on the left side of the grip frame, and a V stamped on the rear surface of the cylinder.

Bill