If tightening the strain screw does not solve the problem ( it will 90% of the time) a little trouble shooting trick is to loosen screw and take a spent primer ( with the anvil removed) and put it on the tip of the screw contacting the mainspring and retighten if problem goes away you can buy a longer screw for a permanent fix. I honestly had a k frame I did this to and just left the little primer cap on the screw and shot it for years that way