Here’s an example of an extractor in which it was overpolished probably from using a rotary tool. I had this extractor setup as a backup in a gun that ran great for thousands of rounds. After having this extractor fitted I had two FTEs in 250 rounds. Upon closer inspection the backside of the hook was polished and the edge slightly rounded over. It is imperative that this hook stays at a sharp 90* angle.
Forgive the blurry picture it was best I could get out of my phone camera but it should illustrate the point.