How about this: If you're seeing scratches in the chamber of a new rifle, how about sending it back to the maker for correction.
Let the people who built it decide if it needs polishing or replacement.
Light scratches have no effect on accuracy, and the only way to tell if they'll cause extraction problems is to shoot it.
If they do, contact the maker and have them send you a shipping label so you can ship it back on their dime.
If you start polishing, you'll void the warranty and you'll pay for repairs.
When you pay good money to buy something new and it's defective, you don't try to fix it yourself.