Insights Into Corrossivity of BPs -- by Bill Knight

[Lars]

Hello,

I have chosen to post this here because such a large fraction of NCOWS shooters use BPs.

Bill Knight is one of the USA's experts on the chemistry of the various BPs, both the traditional ones like Swiss and the modern ones like Hodgdon's 777.

A few years ago I had an e-mail exchange with Bill Knight about the corrosivity of Hodgdon's 777 and other BPs (Swiss, Dupont. Pyrodex and Goex). Recently I dug out a peice of that e-mail exchange and got Bill's permission to post it here. Bill has augmented this material slightly to include some more recent information about a raw material source used by Goex.

This information is about as detailed as I have seen. Hopefully it will be of significant interest and value to some of the BP shooters here. Please note that this material is limited in scope to corrossion. It does not discuss any other aspects of BPs.

Enjoy,
Lars

From Bill Knight,

I saw your posting on the SASS Wire regarding questions on the relative corrosiveness of Triple Seven.

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Any powder using potassium nitrate as an oxygen source is capable of  rusting/corroding various metals under certain conditions.  These powders  produce potassium carbonate as a primary solid product of combustion. Under certain atmospheric conditions this potassium carbonate will cause  rusting of ferrous metals or leaching of brass alloys.

When the R.H. is 30%, or less, the deposits of potassium carbonate are non-hygroscopic. Without sufficient moisture the potash will not form an electrolyte solution on the surface of the metal. Above 30% R.H. the  potassium carbonate, or potash, begins to pick up moisture from the air. As the R.H. rises the amount of water picked up by the potassium carbonate increases.  Once
"damp" it forms an electolyte.  This causes a uniform surface rusting of ferrous metals. On brass it will leach copper from the alloy which gives the green colored deposits on the surface of the brass.

Under the microscope the surfaces of the metal show a uniform removal of surface metals without signs of any pitting.  I have used my computer microscope to watch this uniform metal removal over periods of time.

When you have a powder's combustion residue with any traces of a chloride, such as potassium chloride, you will then see scattered pitting of the surface in addition to the uniform surface metal leaching or rusting.

When Hodgon formulated Triple seven they greatly reduced of amount of potassium perchlorate compared to the amount found in Pyrodex, about 17% in Pyrodex, based on the patent covering Pyrodex.  I ran Triple Seven against Pyrodex and the Swiss BP on mild steel plates and on sheet brass and sheet copper. The extent of surface leaching was the same with all three powders.

All produce potassium carbonate as a primary solid product of combustion. The Swiss use a chloride-free grade of potassium nitrate so there is no evidence of pitting.  Triple seven produces a few widely scattered pits in the surface of the metals.  Pyrodex produces extensive pitting of the various metals' surfaces.  Essentially, the extent or degree of surface pitting simply reflects the chloride content of the respective powders.

But your Aug. 4, 2003, 8:03 AM posting regarding the different grades of steels is correct.  Some steels being more corrosion resistant.  The mild steel used in some muzzleloading rifle barrels is one of the least corrosion resistant steels.  In most cases, the harder steels are more  corrosion resistant.

So the whole issue is clouded by what sort of steel is involved and differences in climate produces varying results with the same powder.

Regarding your comments on Du Pont and Goex. Mixed bag with them.

Ever since WWI the U.S. black powder industry was at the mercy of their raw material suppliers as far as ingredient purity goes.

From the early 1900's until 1986 almost all of the domestically produced potassium nitrate was made by the conversion of synthetically produced sodium nitrate.  Generally, this potassium nitrate would be  0.4 to 0.5% sodium nitrate.  This gave a powder with an affinity for moisture greater than if the potassium nitrate is free of sodium nitrate.

In 1986 the largest producer of potassium nitrate in the U.S. began a process wherby potassium chloride is reacted with nitric acid to yield potassium nitrate and free chlorine. This process gives a 99.0% conversion effeciencty.  The plant produced mainly fertilizer grade potassium nitrate.  This was used at Goex's Moosic, PA plant.  This source contained about 0.4% sodium nitrate and a fraction of a percent of unconverted potassium chloride.   This company ceased operations in 2000 which ended potassium nitrate production in the U.S.  GOEX was then forced to use imported potassium nitrate.  The new source is of a higher purity compared to the old source.  This source appears to be free of any sodium compounds and chlorides. In most respects the powder presently being produced by GOEX is superior to the Du Pont it replaced.

The thing that must be pointed out is that any powder based on the use of potassium nitrate will yield a combustion residue capable of rusting/corrosion under specific conditions of climate.

So your analyses of differences in steels is 100% correct but throw in differences in climate conditions as an additional variable in this.


Regards, Bill K. (aka. Dutch Bill)

[Will Ketchum]

Very interesting!  Does Bill ascribe to the theory that the BP of the 18th and 19th Centuries was better than what we have today?

Will Ketchum

[Lars]

Will,

I don't know specifically about Bill.

The BP shooters I rely on most consider that Swiss is a close modern counterpart to the best of the old BPs. I agree, based on my more limited experience. The old Dupont and Goex sure don't measure up to Swiss. Also, the old, very time-proven BP bullets for calibers like 44-40 and 45 Colt don't work long with low quality BPs like Goex, Elefant, KiK but work really well and for at least close to 100 shots (in good smooth bores) with Swiss, another indication that premium quality BPs were in routine use. See articles by George Warnick and me in Nov/Dec 2005 The Shootist.

The BPCR shooters seem to find very time-tested ways to concoct some really excellent BP loads with Goex -- some at least remove the fines from the powder, even seive it for uniformity of grain size, use classic old BP bullets that carry lots of really excellent lubes (or modern varients of the old, time-tested designs), use blow tubes, etc. Still, Swiss seems the hands down preferrence -- that alone tells me that Swiss, at least, is in the same quality class as the quality BPs of old.

As best I know/hear, the BPs of old spanned a wide range of quality. The schutzen and long range shooters of the late 1800s would have gone for the best BPs they could get. So would the makers of hot, new calibers -- like 44-40. I doubt that the guys toting well used Civil War muskets had much basis for seeking the very best gunpowders. I think that Lewis and Clark took some high quality powder with them.

FYI, I understand that Republic Metallic Cartridge Co. is coming out with an authentic BP loading for 44 Russian.

Lars

[Fox Creek Kid]

Lars is correct here. I know Bill and he is a certifiable genius when it comes to BP. As a matter of fact he is getting ready to test a new BP from a new producer as we speak.    Bill & I compared notes 6 or so years ago about the "break point" of BP and humidity. It's 35 - 40% relative humidity if you must know. Below that you can't keep fouling soft. At 70% humidity fouling becomes deliquescent, the sloppy slurry mess BP shooters love to see in their bore. The main secret to quality BP is the charcoal, buckthorn alder being probably the best as it has approx. 14% creosote if I remember correctly per Bill.

[Dr. Bob]

Lars,

Thanks for sharing this information with us.  I shot a lot of BP in muzzle loading rifles when I was young, but never loaded it into cartridges.  Looks like I need to find some Swiss to use in my firearms. [Guns are artillary! ]

FCK,

Thanks for your additional info.  I really appreciate the wealth of knowledge here on the NCOWS board at CAS City!

Marshal Hollaway,

Thanks for providing this forum for all of us!!!

[TAkaho kid]

Thanks Lars,

Bill Knight (aka The Mad Monk) always has good insight. There is so much we have lost to time and so called progress! What makes it worse is we keep trying to apply our knowlege of today to yesterday when infact we should strive to start with a blank page then build from there. (i.e. get to an 1880's when black powder was THE only powder.) Then start rationalizing the problem. Bill does it from a strictly scientific direction which is great. It bypasses all the myths and prejudices.

As for purity of materials, almost all powder mills of the 19th century imported thier raw materials, Sulfer from Sicily, Potasium Nitrate from India. While it was already high quality stuff many, such as the American Powder Mills in Mass. did thier own refining to thier own standards. In fact the Oreinta Powder Mills in Maine had an extensive charcoal operation. This of course makes a huge diffrence in the powder quality.

A great description of this process can be found in an article by Jane Austin titled "Highly Explosive". It was in the November 1870 issue of the Atlantic Monthly The story follows a young lady named Miselle as she tours the  American Powder Company mill in Acton, Mass.

The individual pages of the article are GIF files. Simply click on the page you would like to read. Or, if your savey you can import them into a PDF file. note that the university holds copy rights to this material.

http://cdl.library.cornell.edu/cgi-bin/moa/sgml/moa-idx?notisid=ABK2934-0026-95

I originally posted this over on THE OPEN RANGE but figured you folks would enjoy it as well.

[Lars]

Will,

There is another answer to your general questions about late 1800s BPs versus those made today. It is at
http://www.theopenrange.net/forum/index.php?topic=1900.0

You might find it interesting to note that the quality of BPs then as today range from low to high, with some folks actually using a "firecracker" powder.

Lars