Sam,
Thanks for the write-up of the test.
I've gotten better results from all the Alliant Reloder powders in recent years than when I first started cold-weather testing 20-some years ago. I suspect they learned something when they had to change the formulation of RL-15 for military use in the late 90's. 15 used to be really bad in cold weather, but became pretty good after the military testing.
Kinda surprised about the H4831 result, as I haven't seen that much change with any of the Extreme powders when used in typical loads--and 150's in the .270 have to be considered a typical load. One thing I'm wondering: Was the test in the same sort of light conditions as the last warm-temp chronographing you did of that load? I've seen Chronys give different results in cloudy and bright conditions.
The photo of the dashboard also looks familiar! Lately I've deen taking two new batteries when doing cold-weather testing, and switching them out for each string of shots. In between I put the cold one in my shirt pocket, inside my coat, to warm up.
