outdoorsmen
If you are using a bronze bore brush you will continue to get black patches. The brush rubbing the bore metal will produce a black residue.
I do not even use the brush - a lot of peole do and it does work but for me it usually is not necessary. After you have completed using the brush then complet your cleaning without the brush - eventually you will get all the black - then grey material out.
Which powder are you using? if you are using a Pyro it will take a little more to get it out...
What I normally do is start with straight regualr windex patches. Usually take about 3-4 patches and then they come out fairly clean. Then apply bore solvent with a bore mop, let it sit then go back with windex patches. I also use a lot of water but it really is not necessary it is just a security blanket for me. After the last round of windex patches, clean dry patches to dry the barrel, When i am sure it is clean apply the lubricant of your choice. I use Slip 2000 but there a ton of good ones out there.
Hope this helps a bit...