Yes, every one of my ARs leaves scratches on the bullet when I eject an unfired round.
One way to determine if the scraches occurs during loading or ejection is to do this. Remove your extrator from your bolt. Re-assemble the rifle (minus the extrator). Insert a loaded magazine and chamber a round. Remove the upper from the lower. Using you finger, remove the carrier. With the carrier out, you will be able to carefully removed the round from the chamber. If there are scratches on the round, it occurred during chambering. If no scratches are present, then the scratches must occur during the extraction process.
SEVERAL DISCLAIMERS -
This advise is very dangerous.
I have never chambered a live round with the extrator removed from the rifle. But, in theory I do not see any harm that could occur from doing this.
Be aware that you are experimenting with a live round !!!! You must make sure the rifle/barrel is pointed in a safe direction at all times.