Howdy
I would check for burrs.
Years ago I had an Uberti Cattleman I bought used that exhibited the same behavior. The first time I loaded it with live ammunition the cylinder froze and I had a heck of a time rotating the cylinder to unload it. It turned out a burr was raised around the hole in the recoil shield where the firing pin protrudes through. As the hammer falls on most single action revolvers, the firing pin is free to wiggle up and down a little bit. This is so it can 'find it's way' through the frame. The arc the tip of the firing pin travels makes this necessary. Repeated firings allowed the tip of the firing pin to displace some frame metal up and cause a burr.
Anyway, the previous owner had fired it enough times (or just played with it dry firing) that the firing pin had raised a burr around the hole. The burr was scraping right across primers, which was pretty scary.
It took more than just laying a file across the burr to remove it because the phenomenon continued to happen. So I took a very long drill and taped it off so it would not hurt the bore. I inserted the drill down the bore and very carefully
turning it by hand I created a bit of a countersink so the burr would not rise above the surface of the recoil shield.
This is another Uberti Cattleman I still have that I gave the same treatment. Yes, it is a little bit crude, but it did the job.
Which, by the way, is why Colt installs a hardened plate in the recoil shield so this will not happen.
I don't know if your revolver has a hammer mounted firing pin, but if it does, this may be the answer.
