I would not use a brass bore brush . Instead take an old nylon bore brush , wrap a piece of chore boy around it . Chore Boy is " pure " copper , not like the after market ones that are steel coated with copper . You can usually find it at Ace Hdwe or Walmart . a brass brush over time could increase wear in the barrel . just my opinion .
If when cleaning a revolver that has fired cast , if I remove a few flakes , I don't consider that a leaded barrel . When I have strips an 1" long , then I have a problem .