Shooting technical advice
Most phosphor bronze brushes are a relatively tight fit in the barrel, but not so tight in the chamber, so the danger is pretty minimal.
For cleaning chambers you can get a soft brass chamber brush.
If you clean your gun after every shooting session, vigorous to-and-fro scrubbing with a phosphor bronze brush shouldnt be necessary.
The brushes also soften with use, so an old, well run in brush will be kinder to chamber and barrel walls than a new one.
Personally, rather than using a to and fro scrubbing motion with the brush, I tend to pass it through the barrels from breech to muzzles with a screwing motion, allowing it to exit the muzzles before withdrawing it.
This seems to be quite effective.