I don't think the extractor would affect anything but the cartridge base, not its rim.
Try this; Take a permanent magic marker and make marks near the rim of a few loaded cartridges at the 12, 3, 6, and 9 positions. Mark one of these lines with an additional "T" for Top and chamber the round making sure that the "T" mark is right a the top position. After firing, see where the shaved area is in relation to your marks. This will help you determine which of the gun's components is acting on the spent shell.
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