Smith & Wesson is showing a new model 640 revolver at the 2010 SHOT Show. The very popular 640 is a five-shot, .357 Magnum “hammerless” revolver. S&W tweaked it for 2010, adding several new features that should prove to be popular.
First off, the old fixed sights have been replaced by a set of tritium, three-dot sights. Additionally, the sights are now dovetailed into the frame, meaning you can replace them without major gunsmithing if you so desire.  These sights are a huge improvement over the standard plain ramp and shallow notch found on the previous 640 revolvers.