When I made my Kibler rifle, and posted images here, some were interested in the process I used to achieve the dramatic and flamboyant curl. So I posted a thread on that subject and it should be available in the search function.
The grade of paper I used, trying to recall from memory, was likely around 320 or maybe 400. I certainly didn't go to 600. If you use that very fine paper, you have a tendency to slick over the surface of the wood which resists the penetration of the solutions you apply, namely tannic acid and ferric nitrate. Some here like to use scrapers which leaves the wood perfect for the absorption of the stains and will definitely yield the most dramatic curl. Before applying tannic acid, I whisker with a new piece of 320 a couple of times. Then I apply the tannic acid and ferric nitrate, and when dry, whisker again, cutting right through the colour to expose the curl. The vivid stain will remain in the curl and will be virtually impossible to remove with sandpaper. And the oil you use to finish will make the curl pop when you wet it down.