Sounds like you're putting movement into the gun at the moment of discharge. At least your errant shots go consistently to the same place. Dry fire or ball-and-dummy practice is warranted. The ball-and-dummy drill is this: Load a live round into the cylinder, skip a chamber and then load two live rounds next to each other. Without looking at the cylinder, give it a little spin and close it. Start firing and when the hammer falls on an empty chamber, the gun should remain almost motionless. Any gross movement will be seen easily.