This was a once fired hull, and it didn't look like that when I loaded it. We shot 100 of these shells and I reloaded them with 7/8oz lead #7.5, TGT-12 WAD, 21.2g of International Clays, WIN209 Primer. 8700psi / 1350fps. from the 100 shells I loaded I got maybe 5 that look like this.
I've seen brand new shells come out like that. Not really uncommon to see that on reloads either. Changing powders might help, but I don't worry about it, since it does not seem to have any adverse effect on the performance. When the crimps get worn/weak, I toss them. Even sooner if something else looks wrong. As long as the hull is not weakened, it's just a cosmetic thing.
An exception I have found is in the loading and firing of the old style AA. The pattern with them is a fairly uniform Blacking/browning of the crimp area. It seems the old plastic used by winchester was a bit more resistant to the burning seen on the newer hulls.......... Larry