As the others said, definitely clean them, dirty cases can be really hard on the sizer die. In the tens of thousands of pistol rounds I've reloaded (38 Spec., 357, 44mag & Spec., 40 S&W, 45 ACP, 38 Super and 9 MM), I have never trimmed a pistol case. Since they are straightwall, they don't stretch like a shouldered rifle case does.