I generally use a 10ga bore brush for heavy 12ga barrel cleaning. I just buy the bronze ones so they won't hurt my barrels any. The 10ga brush is also great for cleaning out the chamber area. I use a standard 12ga brush on choke tubes.
Not quite sure which style of brush you're looking for. They make several different ones and I hear good things about the "tornado" style but haven't tried one yet. I'm waiting to wear out my existing brushes before trying something else.