Welcome aboard! Do you mean preparation of the exterior prior to blue or rebluing or polishing of the bore? You may have to come back and explain exactly what you want to know.
I do know that the prep for oxidation bluing doesn't involve a superfine polish but rather a consistently fresh and clean surface achieved with moderately-fine abrasives. The degree of polish may be higher for hot bluing I suspect but don't know for sure. As to the barrels themselves, obstructions are encountered (ribs) in most cases of both double barreled and modern single-barreled guns. I don't think the problems of application of abrasives would be different. Particle blasting is also a finishing method on modern barrels.
As for polishing bores, I believe an abrasive-loaded lead lap or bob was used traditionally. If "powered" or rotated, the pattern of fine scratches would be largely transverse to the bore. I've also seen mention of French guns having bores polished by a simple back and forth motion of the lap in which case the pattern of micro-scratches would be parallel to the bore. Possibly done this way in the hope of producing less leading of the bores.
jack
