Musings of Dutch Bill on Pyrodex, etc.

[Cuts Crooked]

My Good netizens-

Here is a Giant Wall of Text discussion of powders and subs, Snips from the threads of Dutch Bill,
chemist and consultant to Black Powder Manufacturors;
circa May 2007 and April 2009, as originally posted on "The Open Range":
it has been very gently edited for readability
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Pyrodex is a mechanical mixture.
The ground ingredients are mixed together.  A bit of water is added to cause the ingredient particles to agglomerate together.  A key point is how you control this agglomeration process to give the "grains" of powder.

You will note that most of the bp subs have a low density.  That is to say that for a given volume they will give less weight compared to the same volume of black powder.  The one and only exception to this was GOEX's Clear Shot and it was not made by this agglomeration process.

On the thing about it being a modified black powder.

The original patent issued in 1978 to Pawlak et al. described a gas generating composition of 30 - 82.5 parts by weight of an oxygen contaqining oxidizing agent, 14.5 - 45 parts by weight of an organic carboxylic acid or oxidizable derivative.

No that approach alone gives a slow burning gas generating composition.  Not suitable as a propellant composition for use in guns.

So to speed up the combustion you replace a portion of the potassium nitrate with potassium perchlorate.  This holds 4 atoms of oxygen compared to 3 atoms of oxygen with the potassium nitrate. This gets you up into the realm of propellant powders are far as burning speed, gas generation and rate of gas generation.

When you look at the propellant composition you see 9 parts of charcoal and 6 parts of sulfur.  These two items might be thought of as window dressing.  The powder would work without them.  But their inclusion would make it a modified black powder to most folks.  But they are not really needed to make the basic patentable concept work.

Lucky Ed Pepper is correct in that both the sodium benzoate and the charcoal will act as fuel in the mixture.  But again, It would work without the charcoal also.

The mixture of potassium nitrate and potassium perchlorate is necessary because the sodium benzoate is not overly reactive.

To drift off here.

When you formulate a bp sub there are any number of things that can be used as a fuel.  The usefullness of one of these fuels has a lot to do how reactive it is when it burns. A good example of this issue of reactivity is found in sugar used in sugar based explosive compositions.
If you make a propellant powder out of a mixture of sucrose and potassium nitrate and one out of fructose and potassium nitrate the fructose sugar will win out in burn rates in a propellant powder.  Fruit sugar (fructose) is a monosacaride.  Cane sugar is a disucaride.  In a disucarde you have two sugar molecules joined together.  During powder combustion you would have to split these two sugar molecules apart in order to get them to react during the combustion process.  With the monosucaride you have but one sugar molecule and you don't have to separate it from another one before it will burn.

Lucky Ed also comments:potassium chlorate was very sensitive to impact when mixed with hydrocarbons.

That is true.  The perchlorates being only a little less sensitive to impact shock ignition compared to chlorates.
When Pyrodex first came out and it became known that the formula included a healthy slug of potassium perchlorate there was concern that this powder would be more impact shock ignition sensitive compared to black powder.  Potassium perchlorate is a low-order detonating compound. But when you mix it in with a bunch of other things it is now longer capable of going low-order detonation.  You simply cannot start or support detonation waves in a mixture such as this.  Compared to potassium nitrate, the potassium perchlorate simply provides more oxygen in a shorter period of time.
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One of the driving forces behind the subs is to produce a powder equal to black powder in ballistic performance without having to use the traditional black powder manufacturing machinery.  Described in the various patents as being highly dangerous machinery.  So all of these sub patents then go on to state that the composition covered by the particular patent can be made in relative safety without the dangers inherent in black powder manufacturing machinery.  But then every sub that has come on the market has suffered "incidents" during their manufacture.  Some involving serious injury, death and destruction of the production facility.

The Pyrodex formulation produces a composition that has more potential energy than the same weight of black powder.  So you could not use it on a weight to weight basis.

Except for the now defunct GOEX Clear Shot the others are made by simply agglomerating the ingredients into lumps resembling grains of powder.  Low in density and rather porous.  They are not press densified as is done with black powder.  With black powder if you do not press densify and then polish the grains to a certain minimum density you end up with a powder that does not give good accuracy in a firearm.  With black powder the shot to shot uniformity is more than a bit critical of how well the powder has been press densified and then polished to an even higher density.

With the subs, ideally you formulate the powder to give this volume to volume relationship rather than weight to weight to mitigate the differences in loading density.

This is something that was not seen in Clean Shot or APP.  Low in density but not formulated to make up for it.
In a patched ball rifle the Clean Shot and APP were very weak compared to the same volume of black powder.

Now when you start loading these low density powders behind increasingly longer bullets you see the difference between black powder and the particular sub diminish.  Light weight projectiles are best moved by a powder that gives gas and a lot of heat.  As you increase the length of the projectile, increasing its weight for the same diameter, the slower, cooler burning subs become more practical.  They rely on producing greater amounts of gas but at temperatures lower than those seen in black powders.

To again quote LARS:
"At least in cartridges and percussion muzzle loaders with conicals, I have always got the smallest groups and least visible fouling when I compressed Pyrodex heavily.  Sometimes about 15-20% of its original volume."

In effect, you are press densifying the charge of Pyrodex in the cartridge case.  At those percentages of compression you are forming the grains into what becomes a solid charge.  In effect, a pellet formed in the case.  This is possible because the original grains were not produced from previously press densified material and grains formed by simple agglomeration have little mechanical strength compared to black powder grains produced by the traditional machinery. By pressing the grains into what is a solid charge in the case you are promoting uniform ignition and flamespreading in the case.  One pellet will burn and ignite almost exactly like the last.

Now keep in mind when you do this that there are certain cases you do not want to do this in.  In the .45-70 case you want to be careful as to how much you compress the powder charge.  If you compress the charge to the point where it completly fills the case as a solid non-porous charge you could find yourself in serious trouble.

The .45-70 case has a slight taper from case head to case mouth.  With a solid charge conforming to the inside of the case you have no means for any gases to get around the charge in the case.  You are igniting the rear face of the solid charge.  It begins to evolve gases.  Pushing against the rest of the solid non-porous charge.  As the pressure builds between the case head and the rear face of the burning charge, with no avenue of escape for the gases it simply wedges the solid charge more tightly into the tapered case.  You may expect to see cases that look as if they had seen very high pressures around the case head and primer pocket.  If the action is one of the weak ones you may seen the gun fail.  This has been the case with a number of original trapdoors that were loaded with highly compressed charges of Pyrodex in the standard case.

In straight-side cases it has not been seen to be a problem or danger.  In bottle-neck cases you have a difficult time compressing with enough uniformity to form a solid non-porous charge in the case.

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I recall the old corrosive primers in surplus military ammo.  Corrosive due to a fraction of a grain of potassium perchlorate in the primer composition.

So then we have Pyrodex which is about 17 parts of potassium perchlorate.

The NMLRA had been lobbied to call it a "replica" black powder.  The term "substitute" would infer that while it can be used in place of black powder it is not up to the standards of a good black powder.

It will work as a replacement for black powder but you must clean the gun well and quickly.  And then check it again a day or two later.

Pyrodex residue can be pure hell on fired brass if you leave the fired cases uncleaned.  While the "potash" in black powder will tarnish brass and cause light surface corrosion the potasium chloride in Pyrodex residue can eat holes in the brass if one is not careful with the fired cases.
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First we will look at the black powders.

Goex prior to late 2000 was more corrosive than the other brands on the market at that time.  This was due to the grade of potassium nitrate they were using.  Their long-time supplier folded in 2000 so they had to switch to potassium nitrate produced in Chile.  Their long-time supplier had been shipping them a fertilizer grade of potassium nitrate while telling them it was a technical grade.  They refused to listen to me when I told them that back in 1984.  But at the same time they had no choice.  There was no other U.S. producer of potassium nitrate they could buy from.

Then in 2001 they got their charcoal problem in hand.  After they closed the Moosic plant their long-time charcoal supplier was pulling a fast one on them.

But as it stands now the major brands of BP, GOEX, Schuetzen and Swiss all use a grade of potassium nitrate where the chlorides are measured in parts per million.

On to the subs.
APP, Shockey's Gold, Pinnacle and Black Mag are based on ascorbic acid and potassium nitrate.  Only Black Mag's patent shows the addition of potassium perchlorate.  Which makes its residue more corrosive than the other 3.  APP, Shockey's Gold and Pinnacle are all made by the same company.  So there is really nothing that makes one really superior compared to the others.

Blackhorn 209 was handed to me.  The mfg. claimed it was not a smokeless (nitrocellulose) powder.  So I had at it in the kitchen with different solvents.  Turned out TO BE a nitrocellulose powder with 17 parts of an unidentified chemical used to tone it down in the gun.  The unknown chemical is highly soluble in water.  I just saw no need to spend another day or two in the kitchen to identify it.  And given the price per pound I figured it simply was out of the picture.  After reading a post or two in this thread I might just take another look at the 17 parts of the unidentified water-soluble chemical and see if that would cause corrosion.


With Hodgdon we have Pyrodex and Triple Seven.  The whole patented concept in Pyrodex was the use of sodium benzoate with potassium nitrate.  But to get the two to react fast enough to make it a usefull firearm propellant they had to heave in something like 17 parts of potassium perchlorate.  When the powder burns the potassium perchlorate simply gives up its oxygen and remains as potassium chloride.  ANY chloride will be most corrosive in the gun.


Onto 777.
The patent on Pyrodex ran out a few years back.  Then the in-line ML hunting crowd wanted faster powders.  A big push came when the plastic sabots came into use in the in-line ML rifles.  That 17 parts of potassium perchlorate that was converted to potassium chloride causes a lot of grief with tight fitting sabots.  The little crystals of potassium chloride are scattered to the bore.  When you would push a sabot down the bore the crystals would embed in the plastic.  So you would reach a point where you could not get the sabot down onto the powder charge.

So what we see in 777 is a change to sodium dintitrobenzoate sulonate.  Think of it as going up a notch in benzoates.  This dinitrobenzoate is HIGHLY reactive with charcoal.  So there is no need to heave in a bunch of potassium perchlorate to "strengthen" the powder.  This makes 777 a lot LESS corrosive compared to Pyrodex.  When I checked the 777 on brass plates there was no surface pitting of the brass as with Pyrodex.  Hodgdon's MSDS for 777 shows potassium perchlorate.  From what I saw in my steel plate and brass sheet corrosion tests I don't think it has any perchlorate in it.

With this development of 777 Hodgdon can claim that it is an improved version of Pyrodex.  Makes getting it onto the market a lot cheaper than going through it as if it is an entirely new explosive composition.


The thing about potassium chloride corrosion in gun bores is that a lot of times the average shooter would never know it is happening.  You can get a lot of micro-pitting of the bore which gives the surface of the metal a frosted look.  This comes up to bite the shooter if the shooter switches to black powder.  BP fouling will then act as if it is welded to the bore walls.  Simply because the metal's surface is so rough and pitted.


Just keep in mind that ALL of these powders are based on potassium nitrate as a source of oxygen for powder combustion.  As a result they produce potassium carbonate as a product of combustion.  This "potash" is in itself slightly corrosive in the bore.  Anything in the bore that will dissolve in water to form an electrolyte solution will be corrosive.  So this gives all of these powders what might be called a baseline corrosiveness.  Any chlorides present will enhance/increase this base level of corrosiveness.  Potash itself will only cause a uniform shallow rusting of the surface metal.  As soon as you add chlorides you can get pit corrosion that bites deep into the surface of the metal.  be it steel gun barrels or fired brass cases.


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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)

[Dick Dastardly]

Thanks for the post Cuts.  This one should move to the reference section after interest wanes here.  This is good reference material from a very credible source.

DD-MDA

[Bunk Stagnerg]

Thanks Cuts that is very interesting.
I wish someone could find the very good post  by NOZ or MAKO (not sure) about the chemistry of the reaction between petroleum based lubricants and Gun Powder (Holy Black) residue. It was  somewhere on TOR some time ago but I can't find it .
Any help out there?
Again thanks
Bunk

[hellgate]

Cuts,
Thanks for the history lesson of everything I've been shooting over the years. The only powders I hadn't used were Shocky's and Blackhorn209. The Black Canyon was like kitty litter and the ClearShot looked like smokeless ball powder.

[Cuts Crooked]

Whoops, I meant to put this in the Dark Arts!

[Professor Marvel]

Thanks Cuts that is very interesting.
I wish someone could find the very good post  by NOZ or MAKO (not sure) about the chemistry of the reaction between petroleum based lubricants and Gun Powder (Holy Black) residue. It was  somewhere on TOR some time ago but I can't find it .
Any help out there?
Again thanks
Bunk

Hi Bunk
here is Mako's small treatise on the subject

http://www.cascity.com/forumhall/index.php?topic=41064.0

yhs
prof infected