I used 140grns of H-BMG50 300MK 3283fps...went as high as 146grns, too HOT! 3590fps In these big cases, it takes two grains of powder to see any change.
Tried the Re-25, it just didn't like it. I cant rem the exact numbers but the pressures jumped up. Re-25 has been the staple for the 408c-t
I used it with the 250 MK's that was ok. 3500fps Groups were .5 moa