Tom I ran into a similar ordeal this summer. I ended up finding some plastic built up in my barrel. I had to really scrub the barrell with a .50 cal wire bore brush. It's shot great ever since. Over 150 shots sinse that cleaning, only to clean breech plug and change the ventliner every 50 to 60 shots. I do run a brush through it when I clean the breech plug but only one swipe.
Hope you get it all figured out soon.
Hope you get it all figured out soon.