When cocking a single action Ruger, the cylinder locks up and the extra force exerted by fast cocking is absorbed by the pawl, cylinder ratchet and lock. The fast and furious nature of cowboy action shooting can really stress these relatively fragile parts. The usual result is faster wear in these parts which results in the revolver "getting out of time." You can get a competition strut that will prevent this "over cocking stress" that sells for about $92.00.  However, I have invented my own stop that mounts to the grip frame and utilizes the existing strut.

The device consists of a set screw "B" threaded into a base. The base is held in place by a roll pin "A." The existing strut is ground off flat on the end and everything is adjusted to so the strut hits the set screw "B" just after the hammer cocks.   I have put this device all my Rulers. I can install one on your gun for $50.

 Note: I'm not sure how this would work for the New Vaquero, or the Bisley Frame, since they are shaped different.