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Hygroscopic nature of BP fouling

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Col. Batguano

75 Cal.
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Gentlemen;

We all know that BP residue is extremely hygroscopic in nature. It attracts moisture really fast, and the sulfur residue when combined with water and free oxygen in the atmosphere combines to create an acid which starts the rusting on our steel and iron parts right away. The more humid it is, the faster it starts happening. I was reminded of this last weekend shooting my flinter. Just ONE shot on a humid day and the pan was totally covered in moisture (which I of course wipe down for successive shots). So for a "science experiment" on the same subject, I trickled out some BP on a hard surface (concrete in this case) and ignited it. Then again on some scrap angle iron. The only thing left behind was the black and white burn marks from the powder. No evidence of (I presume atmospheric) moisture immediately descending on the place of ignition. Since it was done on the same day (within 30 minutes or so) there wouldn't be much change in the day-to-day variable either.

So there must be something going on here that I don't fully understand. Can someone help me understand why the differences, (or, what I got wrong in the first paragraph)?
 
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In my experience it depends on the humidity at the time you are shooting, Kentucky is a very humid place, but there are many days when moisture collecting in the fouling is not a problem. Here's a good example of that. This day I shot for about an hour, never had to wipe the pan. You can clearly see the white fouling on the lock after this shot, but it never turned to that black soup you get some days.
March'14M.JPG

Spence
 
My guess is that the residue from shooting is much finer in grain size than that from an open burn (think about how badly your gun cokes up shooting blanks or unpatched ball). The finer the grain size; the more readily it will gather water molecules from the atmosphere. On a muggy day, I have to wipe the pan after every shot, because in the time it takes to re-load, the pan is covered with goo. If I prime and shoot quickly, I don't have to wipe, because the priming won't suck up the moisture for a minute or more.
 
Sulfur actually isn't hygroscopic but it acts like it is because of it's fine particle size. potassuim nitrate and especial charcoal are very hygroscopic. Charcoal has been traditionally used as dehumidifying agent because it absorbed humidity from the air.

The immediate residue From combustion of black powder isn't an acid, the acid is formed when water or moisture from the air combines with the sulfur dioxide gas from combustion of sulfur. The immediate residues are hydroxides of sodium and potassium which are extremely hygroscopic.

So what happens is, acid and bases are the byproducts of combustion creating hygroscopic salts.

So when you clean, the PH of soap neutralizes the acids and the water dissolves the salts.
 
Dew points....don't ask me how it works but dew point vary. It's not down to just humidity.
At work I can put hot steel just welded or burnt on the floor. Flip it over a short while later and there will be water underneath it!
As for muzzleloaders. That is why I recommend a natural lubricant be used during and after shooting. Nothing beats a beeswax based mixture. In my humble opinion ofcouse.
 
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