RE: reloading a 300 Ultra-Mag
I have had consistency trouble out of RL25. I had this great load for 180gr Triple X and then ran out of powder. New 1lb got different results. I had to bump the load up to get same velocities. The temps and all were about the same. Who know.
4350, 7878, H1000, Retumbo, RL22, and AA3100 will all be good choices.