What’s the industry standard on how to straighten this out? I’m using a Dillon 650 to load these .357’s. They fit fine in my chamber go no go gauge. Here is a video.
Hard to tell but that looks more like case head separation forming. Drag a paperclip inside a sized but unloaded case. If it hooks on the inside scrap all the brass that has that marking. You are close to having a bad time.
If not the only other thought I have is it has something to do with it being a nickel coated case. I don't load nickel so can't comment any further than that.
^^^ echo that call to check for rings on the interior wall. A bit hard to tell from the video but it reminded me of shoulder dimpling in a bottleneck when you have too much lube create a small pressure bubble. I assume this is a carbide die and you aren't using any lube at all but confirm. Your case length is ok after sizing?