So you are resizing all once fired brass? Not new?
If the picture is of a once fired piece, the ring is the pressure ring formed at the bottom of a fired case, and IME, cases fired in different chambers of different rifles, and resized, could show this "ring". If you section a piece of brass, you will see it just in front of the case head. You will also see where the case has streached to fit the chamber it was fired in. A potential problem of case head seperation in YOUR rifle.
Be careful if this is indeed once fired stuff.
I`ve never seen this with "new" brass and a new die, when ironing out kinks in the new stuff, but maybe I`ve been lucky over the years.
Good Luck.
