You don't switch to the pistol rotor to do pistol rounds and use the same drop tube? Sometimes I can get away with not switching things out but if you run into problems, as you seem to have, you might try changing things out and see if that solves the problems.
If powder is bridging, make sure you have a drop tube with adequate diameter. They are cheap and I have even been known to drill one out if necessary.
Try the pistol rotor for the pistol powder. I haven't experienced what you are seeing but switching might solve the gunk problem.
