Ripp - I've had the same 'feelings' of what I might find with a bore scope.
As to the brush - the bristles of bronze will not remove guilding metal by abrading it, they are actually softer than the fouling - so say some of the 'experts'.
The brush may physically dislodge some powder fouling, but I prefer to use a solvent that disolves it to be removed by the patch.

If any barrel doesn't need the 'fire/clean/fire/clean -etc - breakin, it's got to be the highly evolved bench rest barrels, so painstakingly made, lapped, rifled & lapped again - yet those are the barrels proper breakin of shoot, clean, shoot, clean etc, is suggested for, by the barrel makers themselves.

So - what is needed for a rough, slam/bam/thankyou mam - punched out 100 before lunch type rifle barrel on a $400.00 complete with scope rifle?