I own three rifles that have charcoal blued barrels. One is the mottled color and definitely had a texture in the bore when I first shot and cleaned the rifle. I subsequently scrubbed the bore with steel wool and it is much better. The second rifle has a more uniform blue black coating with less texture in the bore but you could tell it was there. Shooting has removed this so that it is not noticeable at least to me while cleaning. The third rifle has more of an appearance of being heat blued and the finish seems softer, but the rifle was supposedly charcoal blued. The third barrel is still slick and new like albeit blued in the bore and had some black dust that came out with a good scrubbing prior to shooting the rifle. Based on my experience with these barrels. I think results can vary.a great deal based on temperature, length of soak, type and granulation of charcoal packed in the barrel, and the experience of the person doing the blueing. In a heat controlled oven the process probably works every time, if all factors are the same. Few people have access to such equipment. In my opinion they probably.had a method of preventing any damage to the bore. Antiscaling compound such as used by.knife makers or others may be a possibility. Go back and read Flintriflesmith's comments. He had a great deal of experience with this process. Wish he was still here to comment further. Just my thoughts and observations for what they are worth. Tim