Here is a bit of info I ran across first hand.
Single actions do not all have the same grip shape or size.
This will also make a difference where your groups end up.
For example I have an OM BH 7.5" in .45 Colt, with the factory installed XR3-RED grips. Since the day I got this revolver I had fits putting the groups left of point of aim. This occured mostly standing with one hand, but to a lesser extent with both hands, and not at all from the bench.
As years passed I noticed the anodizing was wearing right above the trigger guard. After a while I became aware that I was actually using my trigger finger to support some of the weight of the gun. Thus the wear. After an extended shooting session I would also come home with a sore finger. The extra quarter inch of space between the handle grip and back of trigger guard was throwing me off. Nothing I did to change my grip helped.
Then on eBay I spotted an XR3 Grip frame. I got that and some grip pannels and installed them on my ruger.
It was an instant cure for the problem.
By putting my hand closer to the center of the revolver and closer to the trigger I found that I wasn't using my trigger finger to support the gun. Only to pull the trigger.
This has helped my shooting considerably. Now I just need to practice to get rid of the old habits.