I gave you my honest, real world experience answer.Ya no kidding just like everything else in the world, including educated, helpful responses on forums...
I'm still at a loss as to when/how it was decided that copper was a bad thing.
And how many shooters clean the bejesus out of a barrel, then have to put "fouler shots" through it to get the accuracy they already had before they cleaned it?
All the "fouler" shots are doing is putting the copper back (that you removed) and smoothing out the imperfections.
Which helps with a better fit of bullet to bore, and helps with the gas seal.