Generally speaking,as cut by the reamer is as geometrically and dimensionally correct as that chamber will be.
If,for whatever reason,the surface finish is not so good,sometimes,maybe,its a reasonable compromise to trade some small amount of dimension or geometric form to gain surface finish.
I would choose the correctness of form over surface finish most of the time.
Best!,use a good sharp reamer and use it right and you will have a very good tool finish.That is a good chamber.
If the tool marks are around the circumferance of the chamber,as they would be from twisting a reamer,you do not polish them out by spinning the barrel and holding some abrasive thing in the chamber.The abrasive will quickly adapt to the lines of the toolmarks,it will cut in the valleys as it cuts the peaks.You will round off and blend,eventually,but what you need to do is cross the texture of the cut...stroke in and out.Then you are only cutting the tops off the peaks.Run the lathe as slow as it will go,or do not run it at all,turn by hand and watch your progress..The stoning lines will run in the direction of the bore,across the toolmarks.If you are running the lathe slow,it will make a crosshatch.Now,once you have stoning lines running in the direction of the bore,then you can switch to a finer grit,spin up the latheand now you will be crossing the stone lines you just made.