I have a 4" Ruger Police Service Six, and I compared it to a picture of a 4" S&W Model 10 with Bull Barrel. It looks like the only big differences are the longer cylinder for the .357 chamber, and the ejector shroud. The two guns are very similar. They look like brothers or something. I'm surprised that S&W didn't accuse Ruger of outright copying their design. A very successful design too.