Thanks, JFE. This is helpful. I wonder if you would share some of your 375 load data with me? Also if your 375s are 375-303s do you fire-form or cold form your brass? I'd like to know what the case length ends up being after forming. All of these questions are because I'd like to give my barrel maker as much data as possible so that he can do the neck and throat to suit the bullet I choose and the overall loaded length. It's kind of like a chicken and egg situation -- I'd like to give hime a loaded round as a reference but I have no way of producing one at the moment. I think I will focus on the Lyman 375499 as a bullet choice. I also have a 255gr plain base Lyman for my 38-55 and I can play around with both. I know these are a lot of questions so many thanks indeed.