I guess technically it’s sort of a design flaw with a belted cartridge if you were to radius off the die more at the bottom edge it would not shave off the brass but then again it would not size that area and you would still have a bulgeLikely a swelled chamber but seems to me that a die with a properly radiused base would not do this to a case. Does the die have a sharp corner at the base that could shave off brass? Perhaps try a different die. I had a 7RM years ago in which my brass slowly got tighter as time went on, perhaps 7 reloads or so and eventually had to replace it. The reason was the body just forward of the belt wasnt getting sized and just got tighter with each reload. As mentioned above, the innovative tech die can solve this issue. I never bought another belted case again, never will.