I don't know if we've shared the same problem, but when I was shooting SASS I had four Ruger Vaquero's in 45 LC. I didn't send them out for work because I'm easily pleased with most "Out of the Box" Rugers. I did decide to strip them down and polish the internals with emery cloth and Flitz polish. While I was at it I would install a Wolff spring kit. Things worked terrifically on three of them, but one I was having the same problem you describe. I don't know what I did during assembly, but I got something out of place. Transfer bar? Pawl? Cylinder stop pin and spring? I really don't know, but when I took it completely apart again and carefully put it back together, low a behold everything worked like a champ. It might be something to check? Smithy.