It seems backward, but water is the solution to the pollution in the barrel......it Boiling water heats the steel of the barrel and it dries itself in under a minute.
The need for water is simply to dissolve and flush the salts that are used in the priming, and are spewed the entire length of the barrel, attracting water and bring on rust to the exposed steel.
After a dissolving flush, a scrub with any solvent and patches definitely takes any problems the water might bring on. A light oiling and the barrel is ready to wait for its next use.
Boiling water has always been the best way to clean Black Powder weapons as well.
Im fair to middling sure that any soldier in any Army anywhere in the world had to keep his weapon clean, no different than anyone elses gun, Hunters, Civilians, ect, 'cept that punishment would be a greater motivator, and getting the job done properly was the goal.