I wold urge you to check out Dutch Schoultz' method - here's a link
http://blackpowderrifleaccuracy.com/
Mr. Schoultz is a real life expert on such matters, and his work is, to my mind, the best non- shooting accessory you can get.
I would also recommend that you get a micrometer (I use a cheapie from Harbor Freight) and when you go down to the dry goods store (JoAnne Fabrics, etc.) bring it with you, along with your little notebook.
Do not get anything with any synthetic material in it!! (Don't ask me how I know
… that was before the internet and I didn't know any better) … if you make this newbie mistake, you will get to clean a dreadful mess of melted goo out of your nice barrel … EEeeeeeeeww!
I like pocket drill, which has a very tight weave, but pillow ticking also works well. Get a few different thicknesses and be sure to write down the numbers from the bottom of the bolt. This way, when you get a cloth that works well, you can try to get the same lot number.
I would avoid using pieces of clothing or odd bits from the thrift store for this particular use, because you cannot be sure how they have worn. The inner thighs of your jeans don't get the wear that the knees or seat do.
When you get the cloth home, be sure to wash the sizing out of it - one trip through the washing machine will do the trick - I line dry to avoid fraying any more than I need to, but it's not really that big a deal.
If you ask a dozen muzzle loaders for their favorite lube, you'll come home with twenty to thirty recipes. I would tell you mine, but that would be revealing a deep dark family secret and my 4x great grand mother would rise from her grave in county Mayo and have herself transshipped here to southeast Vermont to torment me. It involved mink oil. (the lube, not the torment).
As with most things muzzle loading, probably the best advice I can offer is (1) only change one variable at a time, (2) be consistent, (3) be methodical, and (4) go with what works best for you and don't get too wrapped around the axle about "what every one says."
Good luck, and Make Good Smoke!