I do have a bore scope I can stick in there. I'll post pictures tonight when I get home as to what I find.If you have a bore scope inspect the chamber for similar patterns as you see on the spent brass. If they look similar you found your answer. Then use the corresponding reamer to dress the chamber. If you don’t have a reamer a diy piece of foam wrapped with 1200 grit abrasive material/ paper with Flitz polish will further finish the chamber and remove the reamer imperfections.