I spent all day on the barrel and bore. Seemed to get a little harder to push it through the forcing cone. used 0000 first then 00 then 0000. Didnt seem to polish it that much. Used Rem oil and sometime dry cleaning in between. I also dremeled the surefire forend and it came out nice. Only took me three hours but it clears the receiver. I hope my polishing efforts worked. I used a dewalt plug in drill. I still see the tool marks from the factory.
Sounds like you did a fine job. I do this to every custom shotgun I build and to every shotgun I clean. No way in hell will steel wool of any grit damage the steel in your barrel so do it every time you clean it. Like Five O said you are only polishing it not boreing it out and this will ensure better extraction. If any extraction issues continue then it may take a bore hone to get rid of that issue. I have read about it on these gun sites but have never had the issue with any of my weapons or any I have built, which convinces me the polishing resloves the issue if done correctly. I build a lot of 870's and rebuild a lot so to not have these issue when others do further affirms the polishing works.
J.D. McGuire, Owner
AI&P Tactical, LLC www.aiptactical.com
Remington LE Armorer
Mossberg LE Armorer