I went to the range today and tried to do a ladder test at the 300 with some Hornady 100g BTSP and some Varget. the sweet spot was 24 - 24.5 grains with the vertical group close to 1/2 inch (avg Vel 2499). All in all the entire group with the 100 grain bullets was better at 300 than I was getting 87 grain bullets at 100.
For whatever reason that barrel doesn't like the 87 - 90 grain bullets. I am glad I tried the 100's, I had about given up on anything heavier than the 75's.