I shoot a 270 in a Rem 700. I load Remington or Winchester brass (depending on lot), I actually got head seperation because i was not watching closely. Ill try to post some pictures up when i get off work.
With new brass i get the same look you get after FL sizing, i wash it in a solution of Salt, Vinegar, and Laundry Detergent (PM me if you want to use this as there are some very special conciderations), then dry and tumble in green lyman media.
Now i am one of those people who gets the most out of everything. I had well over 25 loadings on the brass when i got the brass from my father. He had several loadings on it as well, and it was bought back in 87.
I still F/L size as i have not gotten a Neck Sizer yet. My load i was using when this happened, was the same load for ALL of the previous loadings. 56.0 gn H4831 LC (the old stuff still going through surplus).
It blew a ring about 3/4 around the case right on the spot i saw before and i always see. Like a moron I kept on shooting and payed no attention to my fired brass. Thankfully i did not have any sticking.
Best advice as a 270 shooter i can give you is this. The shiny ring is nothing to be alarmed about. Run a paper clip through your brass every time you fire it. When i feel a ring forming i recycle the whole lot. (I use 12 rd lots). I am going on about 27 or 28 firings on my current brass right now and they all are still running strong.
Bow to the Mighty .270