Copper/ plastic fouling with powerbelts

[johnnybow]

I've come to the conclusion that I am having plastic/ copper fouling with powerbelts out of my t/c renegade flintlock. When I first started using them years ago they were easy to load and now I can only get a couple shots before I can't get a powerbelt down the barrel. The traditional method of soapy water and hoppes after shooting is not getting the barrel clean enough. How should I clean the barrel to reduce this type of fouling? Thanks