Chap, I might disagree with the issue of primers. I find in my Optima the 777 primer to be more consistant than other primers. Only reason I think so, I ran out of 777 primers and used others in the same session and setup and the group rose higher.

I have also foundmy rifle is better suited for the crushed ribbed sabots. I throw a spit patch and dry patch down it after every shot. Big difference for me in groups.

Good shooting by the way!