Strange line on 303 British Case?

[Aussie48]

Exactly BAR if you hold the LEE deburring tool at an angle to "help" it chamfer the outside of the case mouth that is exactly the mark you get, I suspect other deburring tools will give the same result.

How do I know? I did it myself very early on in my case prep, old, crotchety and wanted to get it done faster.

Dick