A picture of it would help. I discussed "scratching" in micro rifling to a fellow who was building a smoothbore flintlock gun over on a different forum. He started off using coarse sand paper as described and the results were very positive. He ended up turning a ram rod into a rifling rod with inserted scrapers and followed his original "pattern" of scratches. The depth was not great, but it was shooting into 4" at 100 yards.