Pipe cleaners, toothbrushand Q-tips dipped in solvent. Finish it off with these 3 items I mentioned above -gun oil-dipping them for all the little nooks & crannies to avoid rust. Put a little anti-sieze grease or auto wheel bearing/ball joint grease on the nipple threads. Just do not cover either side firing hole with grease. All the bore cleaning should be done with a brass or black nylon bore brush.

Use solvents that remove a host of items like copper, lead & plastic. I do not recommend any "weak" solvents intended for blackpowder rifles or Bore Butter/Wonderlube 1000 barrel seasoners.