Re: 300 win mag sierra 220 loads
I have very good results with H-1000 in the .300 but I mostly shoot 190 Sierras and Speer match. I have also had good accuracy with RL-22, but case-life was shorter with the loads that shot well.
I do not believe that your results at 65 yards can be interpolated for 100 yards, just doesn't work that way. No doubt you are on the way to some great shooting loads but 100 yard tests are 100 yard tests. Just like we do not get 10 inch groups at 1000 yards from a rifle that shoots 1 moa at 100 - lots of variables involved.
My .300's like the bullet to be seated as close to the lands as I can, I back off a couple of hundredths. Magazine length can become a factor if you have a long throated chamber.
Good luck with your load development.