03-18-2020, 08:27 AM
I have found that if working with near max charges, temperature sensitive powders are more likely to have issues. The least sensitive powder that seems to work in my .458x1.8 while still providing a usable velocity with a Speer 400gr is IMR 4227. This seems to be around 1.17 on sensitivity charts. I do see minor changes in how the cartridge performs between spring/fall and summer weather. IMR 4227 does seem to have the benefit of probably not being able to get enough in the case to be a real concern. If I use W296 I have to find my max load during summer. If I develop the load in spring or fall it will be borderline unsafe in the summer. Its a little concerning when you start to flatten out the head stamp on a belted case.