They are both Model 22-4. As far as I know, the TR has a special S/N, Thunder Ranch marked grips, and a padded TR case but otherwise are the same.
I believe the non TR model is refered to as the Classic model. I have one in nickel. I prefer the retro-style service grips over the Thunder Ranch Magnas, although I do like Magnas more than Targets.
Mine is in the upper right. I also have the Lew Horton 25-14 3" 45 acp, upper left.