Dand, this is such an important measurement that I think I will go through a more intensive cleaning process before I arrive at my final figure. The bore appears squeeky clean, and I know it has not had more than one box of bullets through it. The lead slug travels easily through the entire barrel, and the lands are clearly defined.
I have read that industrial strength ammonia (10 percent) is a real effective copper remover if your careful with it and don't leave it in place too long. I'll try something like that and track down a micrometer instead of my trusty vernier.