Grips make all the difference in control, accuracy, and pain. I bought the 640-1 years ago, and it is great. In wish I had kept a second one that I bought in a moment of clear-headed thinking, but sold in a moment of empty-headed insanity.
Uncle Mikes Combat Grip rubber work for me, but the same brand of Boot Grips conceal better. I had to try different grips to find what does and doesn't work for me, other than the factory Uncle Mikes rubber.
This 640-1 .357 S&W Magnum J frame works well for me, for the all steel frame version. I load it with Silvertips, which is supposed to be a less than full power load.
The Lightweight series (like the 642) make better pocket pistols, but they are .38 Specials - which can still do well when shot accurately.
Here is my 640-1, wearing some no longer made Fitz Duramite grips. It generally wears this set of grips, or an identical set in black. These grips are sometimes found on ebay or estate sales. The set of grips that is right for your hands will make a world of difference in shooting.
Here is a link you may want to check:
http://www.hipowersandhandguns.com/Getting%20a%20Grip%20on%20J%20Frames.htm