Last night at the range, firing G20SF (all stock including spring), the brass I was collecting all had marks on the rim - looks like coming from the extractor. I can't seem to get a good picture to post but it looks like a small gouge in the case rim - on all of the cases. Ammo was Underwood 165 Grain flat nose ammo, listed at 1400 fps on the box. Ammo shot great but I have not seen this mark on other cases. I have shot local made ammo, Double Tap and Winchester Silvertips with no issues. Curious what would be causing this. The marks look like they can be dressed with a small file for reloading. Any suggestions or ideas?