Hodgdon Extreme line does great. Alliant also has some of their Power Pro podwers. I've been using the 2000MR and 4000MR with good results. IMR 8208 XBR is also a good one, but not for the 300WM.
Glad to see someone else noticed Alliant Power Pro powder seems temperature insensitive.
"Anyone taking up handloading necessarily plays with unknown factors and takes chances. But so does anyone who drives a car,goes to a cocktail party,eats in a restaurant,or gets married."
Jack O'Connor 1963