You can easily ruin a barrel hand lapping. I think its wise to have a bore scope to see your progress. I tried hand lapping a throat of a gun that had heat cracks, and over did it. I didn't know what I was doing at the time. I wasn't too upset, because the heat cracks in the throat area, but had to have the gun rereamed, and everything reset and lost over 1.5" of barrel. I ended up selling the gun. Took a big loss.