Saw a similar discussion previously. Old guy taught me black powder when I started reenacting ~25 years ago. I have a sharps I purchased about the second year in and have used boiling hot water about a dozen times a year on that weapon, live fire, and reenactments. I do use very large amounts, to the point where I can't touch the barrel. It dries within 10 minutes when I then clean it conventionally with Hoppes. I pull the lock and spray it down separately, and completely strip the block each time and ream out the spark channel. So far little or no degradation of the bore. Finish is about gone from carrying it on the saddle. I also use a replica Cook and Brother muzzle loader as a Confederate, and treat it the same way, with little or no deterioration. I believe the trick is large quantities of boiling water to flush it out fast, and then conventional cleaning to remove any remaining residue.
Contempt of congress, 350 million co-defendents