sharps4590 gives excellent advice. There are many products available over the counter and on the internet for cleaning, lubricating, polishing, shooting, etc. I personally use 777 powder and T/C's Bore Butter as a between-outings preservative, but there are many options just as good or better, including some homemade recipes. About the only real "avoid at all costs" is to stay away from petroleum-based lubricants, cleaners or preservatives. They do not mix with black powder - not a safety issue but a mess to clean up.
Also, I've not had good luck with .015 patches in either of my .50 cal long guns. Slightly thinner, .010, works better for me in terms of accuracy. Not a big difference, but noticeable. However, in all three of my .50 cal pistols .015 works just fine and .010 results in low energy and poor accuracy. One of the fun things about these guns is that each gun is a little different, and discovering what works best is a great excuse for making smoke and noise. Anyway, .010 patches are just an option. Start with .015 as that is usually the best choice in the end.
Finally, should you decide to try the synthetic bp substitutes, be aware that 777 should be reduced about 10 to 15% from the real bp charge for your gun. In other words, shooting with 50 gr of Swiss or Goex bp is equivalent to about 42-45 gr of 777.
Go make some smoke.
