Not to pull this thread OT but I have to say that a Snub Nose .38 Revolver probably is a bad idea to break in a new shooter to the round. If you have a 4" all Steel revolver available, something like a Model 10, you will get better results IMO. Once they become comfortable shooting a ,38 Special in the heavier revolver you can move them to the Snub Nose and they will be better off, again, IMO.
No matter what factory load you run through your M642 it will feel stout to a new shooter. A heavy 4" revolver will help that a lot. Also, Like someone said above, Remington 130 gr FMJ UMC ammo seems to feel light and might be a good place to start your tests. Blazer (Aluminum) also feels like a lighter load even though they claim it isn't, especially in .357 Magnum.