might look at AA 3100 and Magpro. They also sell a very slow 8700 that seems to work well in the .300 case. I'm waiting on a couple bottles of Magpro to try some loads in my 270 mag. RL22 and 7828 would also seem like good choices to me. You'll have to email AA for data on the Magpro powder. I think I'd start with 3100 and 7828 as these two are known to work very well. Still 8700 gives very dense loads
gary
As someone mentioned, T870 from T-Bird is the same as H-870. I have used it in my 300 RUM with the same results. Also, I would definetely try retumbo. I have had very good results with it. Good velocity and low ES. It is also very temp stable......Rich