This is interesting. I was performing some very basic PM on my carry 642 the other day (removing dust bunnies, checking the side plate screws, just generally looking it over), and after replacing the grip and inserting snap caps for testing, I noticed I was getting sparks at the firing pin every time I dry fired. I removed the snap caps and I would still get sparks. Not as big, and not every time, but definately still there.
I tested several other revolvers (another 642, a 640 and a 19) and no sparks. I didn't expect any. It seems to be limited to my cary 642. All I can think of is the firing pin is rubbing against the firing pin channel, but why now, all of a sudden? And what changed to cause this? The side plate hasn't been removed since last summer when Denny Reichard did a deluxe action job on it. I suppose it could have been doing this since then and I just hadn't noticed, but that seems highly unlikely.
I haven't removed the side plate myself to futz with the action, as I am not well versed in S&W innards. I'm not sure I would recognize anything out of the ordinary if I even saw it. I can always send it to the mother ship, but I hate to do that unless absolutely necessary.
Any ideas?