My guess it’s the strong ejector spring which is dragging the case on a sharp edge on the inside of the receiver during ejection. It’s not your dies or your chamber I don’t think. Had the same problem. Watch as you eject a case and see where it is hitting on the inside of the receiver.
Call bore tech and get there lug cleaning kit the best product hands down. Don’t use WD-40 on your guns. It will gum up fire controls unbelievable. Use a oil for firearms like bore tech sells. There are other good ones. Never WD-40.