Ogg,
Many methods are out there for cleaning the flash hole of all the fouling. Toothpicks, welding picks (er whatever they're called), etc. I don't worry about it myself, never have any problems.

150yd grouping. Time will tell, the gun chooses the load. I'm sure it wouldn't be hard to grab a 3" group if you have a scope. Tighter isn't out of the question. You might be able to get 20ga velocities accurately with your gun, not sure about it though. All else being equal, I'd guess a ML will be more fun for ya!