What is really wierd is that you have layers of fouling to deal with, copper on top of powder on top of copper and so on and so forth.
The very best cleaning brush is only good for about 100 strokes maximum, then it is toast.
The tips of the brush do the scrubbing, if your brush is too large??????
Montana Extreme Bore solvent used in conjunction with their plastic brushes followed buy the Montana Extreme Copper killer will get your gun clean quick.
If you have a serious build up, then use JB bore cleaner on the plastic brush.