Maybe these marks are oil dents?
When I first tried resizing 223 cases, I had problems with these even when I was ultra careful with applying the lube. In fact initially, when I tried to do the resizing in just two steps, using the full length dies with the stem removed, I got sometimes got worse than dents. Occasionally the whole case would collapse in the shoulder area, and other times a sort of 'inward crease' would form on the new neck, making it useless. The three step procedure I mentioned earlier, using a form and trim died for the first two passes, seemed to work quite well, with minimal losses. With the brass I was starting with (Federal) and the neck diameter of my chamber, I didn't need to neck turn the reformed case.
I made 100 cases, then, as the devil would have it, I picked up a few hundred brand new 222 cases off Trademe, at a very reasonable price. So I needn't have bothered with reforming 223 in the first place. Never mind - it was an interesting exercise.
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