Woodseye
You are a shooting & reloading god. Very informative post.
I have found my best accuracy with 40-grains H-414, Winchester large rifle primers & Sierra 52 grain HPBT bullet. I also think H-414 is a ditry powder but it seem to work better than anything else in my rifle.

driftrider
The best part about that 1.28" group is it will be the largest group you will see for a long time after you find a reload that REALLY shoots well in that rifle.

Good luck,