Originally Posted by TXnorton
If the case had "stretched" at that point, it would have been over length as Robo has noted, and more than likely would have crumpled in the sizing die. I think Robo has it right in that it looks like a scuffmark from the sizing die.
What caliber? Are you using Small Base full length re-sizing dies? What kind of case lube are you using? I found that the spray-on case lubes do not work for me when reloading .223/5.56 cases in the SB dies. I have had to go back to using the high-pressure case lube with the pad to keep from sticking cases in the FL SB .223 die.
Question for others though: If you see signs of incipient or partial case head separation in your fired cases, would that mean you have a head space problem?
On the headspace issue, the answer could be yes or no. It could be the rifle or the ammo. If you set the shoulder back when re-sizing, it creates excessive headspace (ammo problem). If you are using virgin brass or using factory ammo and getting case head separations, I would surely have the headspace checked. If you just once in a blue moon get a separation with your re-loads, I would say no. That area of the case is the weakest point in the brass and is streached everytime it is fired and worked again everytime it is sized. Even with only .003" headspace, it will weaken the brass at that point in time.