The flat spot is before sizing, as it came out of the gun, so the die would have zero to do with the issue.

The longest cases are about 1.145", which is well below the recommended max length. I have trimmed 100 rounds to 1.1415", (I could find nothing stating to what length to trim). Max length is 1.155 in the Lyman book so my trim is well below that now. I didn't want to trim too much and have pressure problems due to deeper bullet seating. All of the trimming is before any sizing, only cleaning has been performed.

Does the trim length seem okay?

I did note that some of the cases were below 1.40" and some had a smaller diameter base than the average so I kicked those out. I am using the WW brass cases that were originally loaded for the 52, they have a single cannalure ring on them.