Welcome to the Forum. I'm pretty sure it must be a Model 27-2 because I don't believe that S&W ever made a Model 28-2 with 8-3/8" bbl. Open the cylinder of your revolver, and look at the barrel cavity where the yoke fits. The model and serial number should be stamped there. You have a very desirable S&W .357 Magnum, and depending upon its condition, a valuable firearm.