John,
The marks on your brass looked somehow familiar, I picked up a couple of cases sitting on my desk and, sure enough, they exhibited the same marks. I shoot three or four different Lugers, and I didn't know for sure which gun the cases came from but I had a suspicion.
So I went to the range this evening, and did some experimenting. I shot a 1917 LP-08, a 1936 S/42 (my regular shooting gun) and my 5" custom Luger. The LP-08 ejected perfect cases; the S/42 seemed to have just the hint of a marking, but only sometimes; and the custom gun produced severe marks as you show above, every shot. As I suspected.
I marked a couple of cases, and inserted them single-shot into the chamber, mark at the extractor, and shot them. The case-mouth gouges appeared 90-degrees anti-clockwise from the extractor, that is, directly opposite the ejector.
Here's the experiment I performed upon returning home--try it yourself, you will see exactly what is going on.
Dismount the receiver group from the frame, insert an -empty- cartridge case into the chamber, and close the breech. Pull the toggle back very slowly. As the base of the cartridge case contacts the ejector, you will see it rotate--yaw--to the left. You should see it actually move into the barrel extension cut for the breechblock slide. Continue to pull the toggle back, and the ejector will push the case out of the breechblock face and it will fall out the bottom of the of the receiver.
Now put the pistol back together, insert the empty case into the chamber again, and close the breech. Put another -empty- case into a magazine, insert the magazine into the gun, and make the experiment again. You will find, this time, that the presence of the next shell in the magazine (or perhaps the magazine follower itself, after the last shot) is what actually pushes the spent shell upward.
If the upward motion occurs before the case mouth clears the receiver cut, the case will contact the inside of the receiver rail and this scrape will occur.
--Dwight
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