Don't know if you can tell in the pic, bit it's the dreaded crack from over tightening the retention screw.
During the last year and a half I had bought three 45's and put them up on the shelf until I felt well enough to mess with them. Bad idea, I should have checked them out immediately,,,,,,.
First bad sign was a sizing die with a chunk out of the lip of the die.
I believe this one can be saved be drilling and tapping for a 450 sizing die retaining nut if I can find out the tap size/thread pitch.