Gottcha with the sling thing I read the manual wrong.
As far as the barrel thing it might be pitting, but it has no other marks any other place. Just like four or five scratches near where the bullet would sit. I think I am going to push a sabot all the way through the barrel and see what it looks like, the plastic part might show signs or marks. Either way their is no other marks on the barrel, it was actually pretty clean.
The jag is not brass. It looks like aluminum or something.