Re: How to clean bronze brush itself?
Since you've asked repeatedly...
This 'cleaning' is a reasonably common process whereby bore pitting is forestalled.
While what could probably be described as bore neglect can have potential accuracy benefits; the processes that can ultimately destroy a bore's accuracy aren't going to up and cease simply because we don't care to take them seriously.
Clean, don't clean, I'm not telling you it's essential. I'm just telling you I have some concerns about bore preservation that lend themselves to cleaning my rifle before corrosive degradation can get itself well and truly set up for a meal of my favorite bores.
As for cleaning brushes, it's simply a matter where I feel it makes little sense to put back into a bore the very crud I just worked so diligently to get out of it. I wipe the rod each time it comes out of the bore, and I flush the brush after each use. Some of that crud is abrasive (Silica, that's sand and/or pulverized glass, is a regular component of primer compounds. The process of primer ignition employs friction, not percussion.), and some may also be corrosive; so I'd rather make sure that once it's out, it stays out.
Greg