@Gtscotty Hoping with careful loading, my Odin will preform as well as yours is showing
Side note, tossed the 40 pieces of once fire Hornady 108 M from the initial sight in and function testing in the Thumbler. A bit of a surprise as around a third of the brass exhibited that slight 'Grendel Belt' discussed, measuring in at just under .001. Suppose I had forgotten what suspect brass they make in Nebraska, learned that about ten years ago fooling with Hornady cases in another project. Thinking I should start looking for some Lapua 220 to convert, and eagerly awaiting other brass manufactures to jump on board with the caliber.
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As a couple others have said, I think you have the opposite of a belt. It's always hard to tell by a single picture but I'm going to guess that if you measure above and below the 'line', the area below measures smaller than the area above. It's from the new cases being smaller in diameter than your chamber, and the top part swelling to match the chamber wall during firing.