You will not damage a barrel with a brush.
Forum Boss: I generally concur, if the person is using a proper bore guide and is not overly aggressive. However, I have inspected multiple barrels showing damage to the edge of the crown caused by sawing back and forth with bronze brushes. I know that many successful short-range shooters brush very aggressively, but some of those guys also regularly re-crown their barrels or toss them after 800 rounds.
Unless there is an extreme time constraint I recommend using a bronze brush in one direction, then removing it after it exits the barrel, and cleaning it with solvent, then putting it back on the rod and entering from the chamber end. That said, there are some barrels and types of fouling where back and forth movement in the throat area might be required. But I think most people, with custom barrels, will benefit by being conservative, if they clean before the carbon hardens.