I recently picked up a old musket, and I am very unsure what to do as far as cleaning. The outside surface of the barrel has thick rough crusty black spot's that appear to be very hard .It does not appear to be pitted on the surface you can see where someone in the past has cleaned some spots off and it isn't pitted in these areas but the black spots do not make the barrel look very good, there appears to be no red rust, just these black spots some are dime size and randomly scattered on the barrel. Is there anything I can do without causing damage? It appears the gun has not been cleaned in a very long time I would estimate at least in the last 100 yrs or so.