80 again would be best, are you out? 180 straight line scratches are better than DA. If a piece of 180 DA sandpaper gets used too long it will polish the metal and reduce adhesion. Most 180 grit papers are not designed for metal sanding and dull really fast. If you constantly switch to fresh paper and keep a nice sharp cut, even 180 DA is OK, but most guys will not do that properly.