I have had good luck buying brushes fron brush manufactures in the states.There are lots of them listed on the internet. Tube brushes come in brass nylon and stainless . Measure the chamber and get one to fit too.I even use a stainless brush chucked in a drill to clean the inside of the heavy plastic 8 bore industrial cases it seems to condition them and makes them easier to roll crimp. I only wish someone would make " Tornado" brush spiral style large enough for an 8ga. in the many years I cleaned riot shotguns in armorys I never found a bristle brush that could even come close to working as well.
