Take the 66-1 to the range and use a rest and sight it in for the ammo you are wanting to shoot. I found that I was shooting 4" low when I used a 130 grain bullet vs. a 158 grain bullet. Once I sighted in to my Model 19 2-1/2" snub, my scores improved wildly while shooting IDPA which is all double action. Use a single action to sight it in and then practice, practice practice using the same ammo.
Good Luck,
Stonecove