So what I need to do is be VERY careful of removing anything other than the accumulated mess, and very fine steel wool is safe for this.
I'll have a go at it.............
I do have another question, related..........
I have never had this happen in any other shotgun. Had a Mossberg 20 ga when I was a kid that I shot so much that the action bars had to be replaced yet it never did this. Same with a SXS 20 ga Browning I had.
Is this gun doing this because of some underlying problem with the chamber?