I went to the range today and when I got back I dutifully cleaned my G35 using the nylon brush that was supplied by Glock. After reassembly I noticed that the barrel had a lot of copper buildup still inside. I stripped it down and re-cleaned with the nylon brush, but the build up was still there. I then took out my brass brush and boy what a difference. My first pass through, brass was falling everywhere and my patches came out black. Needless to say when I was done my barrel was brass free and looking great. I had switched back to the nylon brush from Glock after reading, several places, that the brass brush can be harmful to the barrel. All these places suggested that I should use what Glock basically told me to use. Being new to handguns I went along but after today I think I will stick to the brass brush. Does anybody actually know if this is a bad choice or has anyone hurt their barrel by using a brass brush?