What do you mean it's not sizing and how did you come to that conclusion? Do you mean it's not chambering? If that's the case (lol) do like Modoc says and see what's hitting, I use dychem or sharpie markers. Yes small base dies can be a good thing if they are fat bottom girls.
Also what lube are you using, a lot of the store bought s#!t isn't good enough for really hard cases. Have you ever tried the homemade lanolin/alcohol stuff? Once you have you won't go back to anything else