I've done a lot on my revolver, and I'm still having some problems.
I have completely removed any hint of gunk in any of the chambers. Soaking in Kroil, vigorous brushing, the chamber scraper, all went into getting everything that clean.
The flash gap is between 0.006" and 0.008", without any hint of snagging there. There is no gunk above or around the barrel's forcing cone.
There is no gunk between the top strap and the recoil plate, either.
It looked like there could have been a bur on the firing pin hole, but I ruled that out. If there had been one, I'd have felt it by running the edge of a feeler gauge across it. Nope, no bur.
I completely disassembled the cylinder for the chamber cleaning, so I also got the rim recesses in the cylinder completely clean. And the extractor's recesses were already pretty clean, but I got at 'em with a stiff brush and got them really clean too. I DID find a bur on one of the extractor recesses, but it wasn't much (some metal was slightly displaced inward, and a little upward too), and between bronze brushing and a little careful use o 600-grit sand paper, the irregularity is gone.
Now I have less drag, and it is seemingly only affecting one chamber. It is also apparently dependent on the rim thickness.
Any ideas would be greatly appreciated.