The mark on your fired cases is caused by the "step" in the standard 9mm chamber in Lugers... the step appears on the blueprints... probably a manufacturing shortcut. Modern chambers do not have this ring.
If the "mark" you are speaking of is a dent of the case mouth, this is pretty common in Lugers, but is of no consequence unless you reload. This will shorted case life, but only slightly...
I sell a CD ($25.00 USD for Domestic shipment to North America or $27.00 USD for mailing to the UK and Europe) that contains very good scans of the 1913 blueprints for the Luger... they are an interesting study in themselves... If you are interested in a copy of the CD, please send me a Private Message by clicking on the icon at the bottom of this post showing two stick men shaking hands in front of an envelope... This month, $5.00 of the price will be donated to the Lugerforum operating costs...
