Try this:
Just for grins and giggles, try this:
Mark your cylinder to you can identify each chamber.
Set up a target with 6 bullseyes (the Raging Bull is a Six-shootier, right?)
Load all chambers and index the gun to fire chamber #1 and shoot bullseye #1, then 32, then #3.... and so forth. (and make sure the cylinder stop hand is locked up in the cylinder for each round).
Load up again and repeat. Chamber #1 going to bullseye #1 and so forth.
In this way, each chamber is producing its own group on its own bullseye, independent of the other chambers.
This process just eliminates one variable from a world of variables.
You could also put the gun through this examination, paying particular attention to the cylinder lock-up.
http://thefiringline.com/forums/showthread.php?t=57816
I may be particularly sensitive to the cylinder lockup because I had a SUPREMELY accurate Dan Wesson revolver which locked up in double action OK and in single action if the hammer were cocked quickly, but if cocked slowly, the advancing hand did not rotate the cylinder far enough for the locking hand (cylinder stop) to drop into the locking notch, leaving the chamber close, but not quite, fully lined up with the barrel. Accuracy may have suffered. DW fixed it quickly with no charge, but I didn't have the foresight to test it to see if it actually did affect accuracy.
Lost Sheep