I have used the RCBS Charge Master 1500 combo for the last four or five years. It works great and really speeds up the process. I do not know how excess heat or cold would affect it's operation.

The RCBS powder thrower on my bench is only used for pistol loads (flake or ball powders), but it does a good job. I found that the trick to getting consistent charges from it was to use it consistently. By this I mean using the exactly same motion and force every time I pull the handle. I weigh every tenth load and the charges are very consistent.
Years ago I tried to throw some rifle loads using IMR (long grained) powder and did not like the results.

Merry Christmas to you too!