Time for another 2 cents.. You have received many good comments already..
1) remove lock from gun, remove springs, release sear from notch, rock lock to and fro. Does the hammer flop freely? If not find and fix why not..
2) Is the tumbler loose in it's holes? If the hammer has to much slop it will move around and cause the bearing surfaces to change causing issues.
3) Reassemble the lock, Clean up the inside of the mortis so you start with clean area, Blacken the WHOLE inside of the lock well. reassemble and cycle the a few times, remove and inspect with a flashlight including inside of the sear hole.. Remove any trace of color..
4) Does the cup on the hammer clear the nipple well. Is the inside of th ecup free of any crud, this will act as a pad and can cause miss fires...
Ok so that was 4 cents
Lots of luck..Keep us posted..
Dave