Took my Lyman Great Plains .54 flintlock out to the range today for the first time after following duelist1954's instructions for polishing the bore with Scotch Brite (link
here).
I had the same problem that Mike had, which was the rifle was extremely difficult to load after just 2 or 3 shots because of fouling. With mine, there was a spot about 8 inches down the bore that practically required a jackhammer to pass with a reasonably tight load (.015 patch and .53 RB).
I did what Mike did, and cut 7 or 8 patches from a Stotch Brite pad and ran them down the bore 10 times each with an undersized jag (.36 cal).
Today, I got to 10 shots without noticing any difficulty loading, and went all the way to 13 before I cleaned. I probably could have kept going, but I needed a break anyway.
Success! Thanks, Mike!
Now all I need is the time and place to do a proper sight-in. I have no idea where I'm hitting at 50 yards, but our local range doesn't allow BP on the shorter ranges.