I was having a conversation with a guy at work about gun cleaning. He said he doesn't use the copper bristle bore brushes because they scratch the barrel. Generally I clean my guns right after I use them so I don't have to use a brush but what do you do if you buy a used gun that's really dirty and needs to be scrubbed? Will the copper bore brushes hurt the barrel if you scrub back and forth to get all the crap out? I know it scratches the inside of the barrel a bit but how much does it really matter/affect the barrel? How do you guys clean a really dirty barrel?