I loaded .40s&w for years using WST for my IDPA loads. It is indeed reverse temp sensitive, but manageable. I worked my load, chrono'd it in the spring while temps were in the mid 60's. I always like my loads to be 5 above on the PF, so they came in at 725fps with a PF of 130.5. That summer I chrono'd the same load, and still came in at 717fps with a PF of 129.06, and temps in the low 90's. That following winter I once again chrono'd them at 732fps with a PF of 131.7, and temps in the upper 30's/lower40's. After the first year I adjusted my load for the summer .1gr just to have that 5pf safety cushion for bigger matches. The ONLY trouble I ever had with WST was 2 summers ago I shot a match that had very little shade, and only enough room under the roof at each bay to sit. There for I had to leave my cart with my range bag, and cooler out in the sun. After lunch I had a few really weak rounds that failed to cycle my slide fully. It hit me that my ammo was getting too hot, so I placed my ammo boxes in a pocket on my soft sided cooler to cool them down. Since then I have never had issue.