Beware of brushes with steel core wire going through the center of the brush, especially if the wire is snipped off at the top of the brush, leaving sharp edges.  These can often harm a chamber or throat if not correctly centered.

Our benchrest brushes are made with brass core wire that is fashioned into a loop at the top.  No sharp edges are exposed to the bore.  Extra bronze fill is used and the brushes are made oversize.  Generally they will do a better job of cleaning and last longer.  Whenever possible, a rod guide should be used when cleaning - it will help keep everything centered in the bore.