Old Painless, who runs the famous Box O’ Truth website, has written a lengthly post on AR-15.com about the process he went through restoring an old shotgun. His post includes lots of photos.

Old Painless uses fine steel wool and WD-40 to remove rust. I personally use #0000 steel wool, which is very fine, and gun oil. This combination does not remove gun bluing if you are gentle. #00000 steel wool can be bought but I think it would be too fine.

[ Many thanks to jdun1911 for emailing me the link. ]