Originally Posted by danf_fl
It could be that something is binding up the cylinder or debris in the trigger mechanism.
If S&W is willing to look at it, send it in.
Here's an update. Today I found my 642 is back to normal and the trigger pull is smooth and progressive. I called S&W customer service who told me the 642 is not designed to be dry firing 40 times continously at a time.
The proper dry firing sequence should be 5 shots with breaks (to simulate change of ammo). They said using snap caps and dry fire continously will make the revolver drag on them. The finger muscle will become fatigue and feel stiffer trigger pull while the trigger pull on the 642 does not really change.
In other words, shooting real ammo is different from practicing dry fires.
I'll shoot at the range this week and see what happens.
Does this make sense to your experience?