I was checking my replica barrel and I've seen it has a clear line inside of it. The aspect its like if a BB was rubbed in a straight line all over it. It doesn't have any white residue, but its not smooth as the rest of the barrel, so I was wondering if there is a way to clean/remove that in order to make all the barrel smooth. Both captures where made rotating the barrel for each one, so the line appears on left of one and right of the other, but the line its straight and always on the same spot. Not sure if its easily noticeable on my pics... Any idea how to remove that residue from the barrel?