bronko22000

The tool you guys mentioned was made by T/C and may still be made. I had one years ago when I changed a percussion to flintlock.
I also agree that you shouldn't remove the plug. When I clean my flintlocks, I remove the barrel from the stock, set the barrel breech first in a bucket of hot soapy water for a min. or two, then take it out and remove the flash hole. Then put it back in the water, WET (I repeat - WET) a patch, place it over the muzzle and proceed to swab the bore out flushing the barrel with the soapy water for several mins. While I'm doing that, I have a pot of clean water boiling on the stove. I take the barrel outside and hang it by one of the ramrod barrels on a bent nail and pour the hot clean water down the muzzle flushing out the barrel. Caution barrel will be very hot.
Take it inside and run some patches through it. I dry, use #13 black power solvent, dry, until patches come out clean.
When I'm done I run a patch coated with bore butter through the barrel to prevent rust.
Don't use oil with black powder - the petroleum when combined with burning black powder is highly corrosive and results in a tar like buildup.