Legionnaire, Do you have a specific question about a specific model? As the others have responded the dash number indicates an engineering change to a model. Prior to the time that S&W model numbered their guns, the guns had names like Masterpiece or Military & Police, etc and when S&W made a change they just simple stated 3rd change and so forth. I am a member over on the S&W as are many other here, I'm sure. Go over and visit, it's a wonder place to learn about S&W's; and if your into the Greatest Revolver In The World (I'm prejudice) join the forum. The new and improved Standard Catalog of Smith & Wesson, the 3rd edition, will be out late this year. The SCSW is the bible when it comes to S&W's. Jim Supica, a memeber if the forum and Richard Nahas have historically done a wonderful, wonderful job in putting a tremendious amount of information in a concise orderly fashioned manual. Regards P.T.