What I was referring to is, IF the brass is a little too short, and the case headspaces on the rim, there is an area on the case that may be 'back from the case mouth where the case is tapered prematurely by the case being too short. Then when the bang happens, the case swells to meet the size of the chamber, and because the case is not the same size as the chamber because it is too short, you get more expansion because of the small size difference due to the slight taper in the case as it is designed, but guys, I am NO expert on reloading and chambers and sizing. Just thinking out loud.
