Re: 300 rum
Getcha some 180 Accubonds like Fiftydriver says and then load 1 grain up or down of 95 grains of RL25 and you will be in business! I have done load development for probably a dozen of those 300 Ultras, and that load has worked best in all of them! It's kind of like putting 29 grains of N133 in a 6 PPC, every one of them just love it.
Oh yeah, run a Federal 215 gm primer too!
If it's not far, it's boring.