Listen to what Driftwood has to say. His posts are not just good or very good, but phenomenal! I've said many a time that he should write a book, and I believe others have.
So, it's difficult to elaborate much more when standing in Driftwood's tall shadow, but I do have a few tidbits to add.
I've never had corrosion problems with black powder, but, then again, I clean up religiously after firing, within a few hours. In theory, cleaning up after firing a black powder gun should be easier and cheaper, as water is much more plentiful than petroleum based compounds and at little or no cost. Running many a patch laden with gun oil or Hoppes No 9 after firing a smokeless powder firearm is much more time consuming than running boiling water down a barrel and then following up with patches, although admittedly many that come out quite black, after firing a firearm that was fired with black powder.
Let's start out by saying that IF you fire a 19th Century firearm, and some early 20th Century firearms that were designed for black powder, then fire black powder only! The reasons were given previously in this thread, e.g., the pressure-time curve, but if something was designed for black powder, why substitute anything else? That's like running diesel fuel in your car that runs on unleaded gasoline, if you ask me. Also, as far as black powder substitutes, such as Pyrodex, I have no experience with these, because, again, why substitute anything else? I have heard that Pyrodex is much more corrosive than black powder, but it's only what I have
heard. Again, as I have not had corrosion problems with black powder, then Pyrodex certainly cannot be less corrosive than black powder is. (Admittedly, as a footnote, I do have one experience with Pyrodex. A friend heard I was starting to load black powder rounds nearly 10 years ago now and offered me about half a pound of black powder. I graciously accepted his gift and then used it to fertilize the lawn).
As others have stated, the corrosiveness associated with black powder likely stems from the use of mercury fulminate primers, and not the black powder itself. If I had to hazard a guess, this is why pitting in vintage firearms is often more extensive the first third of the barrel as this was the extent of the mercury fulminate contamination and the remainder was not subjected to as high concentrations of mercury fulminate.
Let's start with some chemistry. Chemistry is always a good approach to understanding something that could be perceived as mysterious.
"Gunpowder does not burn as a single reaction, so the byproducts are not easily predicted. One study[
citation needed] showed that it produced (in order of descending quantities) 55.91% solid products: potassium carbonate,
potassium sulfate,
potassium sulfide, sulfur, potassium nitrate,
potassium thiocyanate, carbon,
ammonium carbonate and 42.98% gaseous products:
carbon dioxide,
nitrogen,
carbon monoxide,
hydrogen sulfide,
hydrogen,
methane, 1.11% water.
However, simplified equations have been cited.
A simple, commonly cited,
chemical equation for the combustion of black powder is
2
KNO3 +
S + 3
C →
K2S +
N2 + 3
CO2.
A balanced, but still simplified, equation is
[126]
10
KNO3 + 3
S + 8
C → 2
K2CO3 + 3
K2SO4 + 6
CO2 + 5
N2."
Source:
https://en.wikipedia.org/wiki/Gunpowder
From the second equation, K2SO4 is potassium carbonate, a white salt which is soluble in water. (Source:
https://en.wikipedia.org/wiki/Potassium_carbonate)
So, run water down the barrel of your firearm, and remove any salts, and corrosion should be prevented. Now I, and others, run boiling water down the barrel of a firearm, and this is to not only dissolve salts, but to enhance evaporation of water, thereby lessening the chance of any rust forming. And then I religiously clean the barrel and oil the firearm. But, it should be stated, it appears that water, of any temperature, will dissolve potassium carbonate, so if one does not have access to water at home, heated to boiling, one should be able to use water from a stream or lake to remove any salts until a thorough cleaning can be performed later, as long as everything is dried. For that matter, coffee from your Thermos could suffice, if necessary.
And, lots of misconceptions out there on the internet. You cannot believe everything you read on the internet. Let's dispel a few myths in an article that comes up early in a search of "how corrosive is black powder".
Here's the link:
https://www.chuckhawks.com/problems_blackpowder.htm
The title: "Problems of Blackpowder". Appears to me there's an agenda.
"A problem associated with black powder is its hygroscopicity. Black powder absorbs about 1.5 weight percent moisture under 75 percent relative humidity at a temperature of 21.1.degrees C. (70.degrees F.) over a period of 24 hours. If black powder picks up sufficient moisture, there is a possibility that the black powder will not burn as fast. High relative humidity may cause erratic behavior. Water may cause the potassium nitrate to migrate out of the black powder and cause corrosion of metallic parts."
Really? What problems? Keep your powder dry. If you load a metallic cartridge, no water should be getting into the case. Remove salts with water after firing. I don't see a problem.
"Black powder is unpredictable in a sense that it can ignite unexpectedly and thereby cause property destruction, injuries, and death."
This is a myth. So can gasoline. If this was the case, why have studies of static electricity and black powder failed to ignite it? Why is black powder now available in plastic containers that could potentially create static electricity? Just have a healthy respect for black powder, use brass reloading components, and leave your cigarette away from the reloading bench, and you shouldn't have a problem.
"Smokeless powder was created as a black powder substitute; nothing could be more obvious."
And how? The pressure curves dispel this one. Also, fill a case to capacity with smokeless powder, as a "substitute", and see how many fingers you have left after you pick up your firearm in at least a dozen pieces.
So, I hope this proves helpful to some degree, in understanding some of the chemistry behind black powder ignition and dispels at least a few myths.