Rough chamber could cause that. It could even just be dirty. Maybe clean the chamber itself, I'm assuming when you say you ran brushes and patches you were referring to the bore. Otherwise the chamber needs to be cleaned up. I'd suggest that you ensure that it doesn't get enlarged outside of saami specs
The horizantal scratches are likely from the case being held by the bolt during extraction and rotated against something in the chamber. Given that it appears to be in the same spot on each piece of brass, I'd inspect that portion of your chamber and you'll likley find your answer.