I have used retumbo in a 338 lm and rl22 in a 257 wby and 7mm RM and h4350 in a 243 win. I have done all load dev in the summer at ~80f, got accurate loads and chronographed them. I then shot and chronographed those loads in -30f where everything was that temp ( as in gun and ammo were in back of truck on the way to the range in the winter. 45 min drive). My retumbo load lost 30 fps, h4350 25 fps and the rl22 loads lost 150 and 120 respectively.
I use only h4350 and retumbo now for any hunting ammo where I'm out in the cold hunting. I will test h4350 in my 270 wsm this winter but I expect it to preform the same.
I often hear people say magpro or RLxx for highest fps but they are of no interest to me if they are slow in the winter where it counts for me. I go hunting when it's cold. Not when it's 80F.
