i had a crap upper that had a really ruff chamber exibited about the same issue as you except mine would also tear a chunk out of the rim
shells came out like this... when they came out
corresponding markings in my chamber
I found a dowel slightly smaller than the chamber diameter cut a slit in it and wrapped a small piece of very fine emery cloth around it.
chuck in drill add some honing oil and make sure to keep drill moving in and out.
This is sort of the extreme end of it.
I started just with a chamber brush by hand.
many people will just use a shotgun or handgun mop with some flitz if it's not as bad as mine was.
It's not hard to overdo it with the emery cloth go slow and check often.
don't do this if your chamber looks relatively smooth and uniform it shouldn't be a mirror finish just uniform.
You may also have some gas issues