After you fire are you working the bolt with vigor as one would when hunting, or are you slowly opening the bolt and finding this damage to the case extractor grove?
Does cycling your rounds through your action do this or is it only when you are shooting?
And that is more than little brass shavings IMO
For the message of the Cross is foolishness to those who are perishing, But to us who are being saved, It Is The Power Of God. 1Corinthians 1-18