If you roll crimp the shorter shell & fold crimp the longer one you will end up with similar internal capacity. However if you put the load checked out for the longer hull in a shorter one & still fold crimp, then you must give it a lot of extra compression. Since the wad was designed to have a certain amount of compression to take up the initial pressure rise of the burning powder I can see a potential for increasing pressure by taking up this "Slack" in the loading process rather than in the firing. Don't know, maybe we're speaking of two different circumstances.
