I just bought a 642 yesterday, my first snubby, after two range trips and about two hundred rounds I learned the following:
The grips aren't great (however I am going to try to shoot another 300 rounds spread out evenly over the next month before I change anything on it).
Over 100 rounds per visit does not work out so well for me, I'm missing some skin on the webbing of my hand.
I shrunk my group size considerably when I forced myself to stop staging the trigger.
It is a hard pistol to shoot well but really rewarding when I do.