Your own source Bill Knight states:
"Potassium chloride is by itself not overly hygroscopic. If crystals of potassium chloride are scattered over the surface of a steel plate they will not began to attack the metal until the relative humidity reaches a certain point. Generally fairly high humidity is required to wet the surfaces of the crystals."
And
"In the case of brass, a film of potassium carbonate on the brass will cause discoloration of the surface of the brass—various shades of brown to black, depending on the humidity. But, the potassium carbonate will not actively pit the brass." --->>> https://www.camp22.org/black-powder-pages/barrel-fouling-black-powder-vs-substitutes
There's are differences between theory and reality.
In some cases the sub. powder may corrode more than black powder, and in other cases the sub. powder may corrode less than black powder if at all.
It depends on factors that may or may not be present, and on the amounts of the respective by -products.
I read a lot of eye witness testimony to catch up on this whole controversy.
There was a great majority of people who never experienced any rust with Black Horn 209, some after many shots and many months without regular cleaning.
That's proven, and it happened in different parts of the country.
Take the same of number of shots using the same amount of black powder and under the exact same circumstances, and those guns very well may be rust buckets if they could be fired at all.
They would need to be swabbed much too often compared to BH 209 for a fair test.
That would truly show the relative potential for corrosion that could be caused by each of the powders.
I hope that you understand what I mean.
Take 100 or 1000 guns and fire the same number of each with one of the 2 respective powders and store them under the same circumstances and see how many of each are left standing.
I have real doubts that black powder would win out because too many people have testified that corrosion didn't happen to their guns shooting BH 209.
The posters were not in a secret conspiracy to hide the facts.
One actually stated that he was going to continue to not clean his gun because of the lack of any corrosion.
Many of these testimonies were posted around the time when the very first reports of corrosion with Black Horn 209 were beginning to come forward in 2008 and 2009, just about the same time when Western Powders started putting a sterner warning on the bottle.
That's why I asked whether placing a gun in a soft case might prevent corrosion.
I believe that it may based on the way that people treated their guns without cleaning and without causing corrosion.
Can you prove that a gun case doesn't offer protection from humidity?
Of course not.
For all we know there could be by-products in the BH 209 residue itself that inhibit moisture absorption, such as an oil base that protects the metal more than we know.
Someone with a nitride rifle posted that he hasn't cleaned his gun of BH 209 residue in over 4 years.
He doesn't doubt that any other gun would rust under similar circumstances.
But can the same be said if black powder were fired in the same gun for 4 years?
That would be impossible to begin with because of his number of range sessions, but there's other parts of the gun besides the bore that could be affected.
Some speculated that maybe higher pressure or combustion efficiency blows the contaminants right out of their bore for the most part.
Maybe in part that's why some BH 209 users only experience a very light brown or whitish film that wipes right off without causing damage.
Someone said that there's a film that seems to be lubricating during loading.
In this case I'm more interested in actual results than theories. and field results over lab tests.
Perhaps there are facts that aren't in evidence, and that your references don't include.
Now that people are aware that BH 209 can cause rust, they clean their guns to be safe.
But that doesn't change the experiences of so many in the past.
Just like with Reece Talley.
And I also posted an example of how unfired black powder may have caused corrosion.