Still trying to move forward.
Today, I checked:
* the hammer for marks where the sear engages. No marks, it looked like new, and very well finished.
the only real thing I noticed is the bore for the hammer is close. Not too close, but if the spring ends
were not exactly square, it might hang up a tiny bit. I really don't know what to say here, just an
observation. I did lube the bore and hammer with dry graphite to see if there's an improvement.
There's really not much more I can do right now. I'll let it set and then chrony it again. If no help then I'm going to go into the firing valve and look at the orings. They're not leaking but they could be sticking. On FX guns with the valve and hammer in the action like the Crown, Dreamline, WC etc and not like the Impact, the valve hanging up hasn't been an issue for me yet, but it's worth checking.
When I replaced the oring the reg fits into, in the action, it was hard and broke in my hands, and one of the orings on the reg adjuster was shot and deformed. So, it may point to an oring in the valve being hard/bad. That's next on my list, maybe a full rebuild.
Just a comment about the oring in the action that the reg sits in. If you let this oring get old and hard, it is really, REALLY hard to get out. It's hard to puncture and you literally have to dig a section out of it and work it out. It is a hard job. If it were me, I'd change that oring ever other year or whatever to keep it from getting hard. When they're soft, and you use good light, you can pop them right out with a long hat pin.
A tip on putting that oring back it, is insert the piston with the spring washers on it. This will keep the oring from going to much below the groove. Then it's just a matter of pusing it in place or pulling it up slightly with a curved pick. I plan on making a piece of plastic the size and shape of the piston height and tall enough to come up to the bottom of the oring groove and then it will be child's play putting it back in.