Use 4-0 steel wool, not 3-0.
Use a little oil with the steel wool.
If scratches remain, try rubbing them out with crocus cloth (that is, jeweler's rouge).
Clean really well, after polishing.
If it's an heirloom gun worth preserving, you could try end-grain balsa wood, with oil.
Balsa is just a little bit abrasive, and may not leave any scratching at all.
Do not use a power tool.