How does the chamber cast look?

Photo of case and chamber cast would help.

A friend brought me a custom Springfield and several fired cases. The fired cases show heavy concave ring just below the shoulder. I take the rifle and cases and tell him I'll see what I can do. No visable ring in the chamber. Fired cases are normal with the exeception of the ring, but I was cautious. I necked down some 35 Whelen cases until the just would chamber and loaded them with fireforming blanks. Still the ring. Very odd. It isn't a step in the chamber, but more of a pinch. It's very deep, but I don't see what made it. Any ideas?

Here's a longshot...

If the barrel was once chambered in .308 Win and then rechambered to 30-06, you can end up with what looks like a ring below the shoulder.

Sam B.
info@fireflyarms.com