This is a chapter out of Ian Von Maltitz's book "Black Powder Testing and Optimization" and is available from American Fireworks News. Go there to read all about it. AFN Link

Chapter 10 -- Turbocharged Black Powder

Introduction

This chapter focuses on optimization methods aimed at producing very fast Black Powder.

Before exploring the various methodologies used to produce very fast powder, it is worthwhile examining reasons why one might wish to do so. It is also worth looking at reasons why one may wish to stay with slower-burning Black Powder. Faster powders offer better performance in certain applications. Slower powders work better in others.

And then there is the issue of safety. Faster powders are generally more hazardous than slower powders. This applies both in their manufacture and in their use.

Fast Powders and Their Uses

Fast powders are used in many different applications, including:

Black Powder firearms

Lift (propellant) for fireworks shells

Propellant for roman candles

Propellant for comets

Burst charges for fireworks shells

Fireworks mines

Fuses

Rockets

Firecrackers.

One notices from the above list that some of the more important fireworks applications require fast Black Powder. So generally, for fireworks use, fast Black Powder is more desirable. Just how fast depends on the application.

Roman candles typically need a faster powder than shells. Comets and small shells need a faster powder than large shells. Rockets may or may not need a fast powder, depending on a number of different factors. Fuses, depending on the type and application, could require a fast powder.

Slow powders have less going for them. Blasting powder generally is a slower powder. Some rockets are better made with slow powder. Slow powder also finds its uses in fireworks such as gerbs, fountains, and drivers. Some fuses use slow powder.

How Fast is Fast?

The term fast means different things to different people. To some fast means Black Powder that is fast enough to do the job. To others fast means faster than anything else in existence.

Black Powder that is fast enough to do the job could be a lot slower than the fastest powders around. Before the modern proliferation of very fast powders, many pyrotechnic enthusiasts successfully launched shells with powders that burned a lot slower than their commercial counterparts. These required more powder, but still worked. The problem of requiring extra powder was offset by differences in cost. Commercial powders, although requiring less material still cost a lot more.

Such slower burning powders worked well for large shells and maybe not so well for smaller shells. They were not recommended for Roman candles. This last-mentioned constraint was one of the main reasons that I aspired to making faster powder - I needed the stuff for Roman candles.

But is there any objective measure of fast? Is there any baseline? One objective measure of fast is to make comparisons with commercial powders such as Elephant and GOEX. This is quite a good objective measure as one can assume that such commercial brands will maintain reasonable consistencies from one batch to the next.

How Safe is Fast?

Fast is not safe!

Fast is highly dangerous. Faster is even more dangerous, both in manufacture and in use. All Black Powder manufacture and use is dangerous to some extent. Making and using faster powders increases oneís exposure to danger.

At one time it was considered prudent to make powders that were just fast enough to do the job in hand. Today this wisdom does not get the attention it deserves. One reason for this is the phenomenon discussed in the next section.

Competition Grade Black Powder

In the last few years a new type of Black Powder has gained prominence in amateur pyrotechnic circles. This is the so-called competition grade Black Powder.

What is competition grade and how did it come about? Competition grade Black Powder is a powder that is considered to be faster than its commercial counterparts, sometimes quite a lot faster. Another way of defining competition grade is a powder that gives top readings in Pyro Golf competitions. What is Pyro Golf?

Pyro Golf is a test mortar that fires golf balls. It is used to test the strength of Black Powder both in laboratory type tests, and in competitions between amateur Black Powder makers. Pyro Golf is described in detail in the chapter on testing.

Before Pyro Golf came on the scene there was no such thing as competition grade Black Powder. Now there is -- inspired in part by Pyro Golf. Other factors did come into play such as more and more pyrotechnic enthusiasts acquiring high efficiency ball mills.

Pyro Golf, with its spin-off of competition grade powders, has had a very positive impact on amateur Black Powder making. It has inspired an interest in making Black Powder that did not exist before. This resulted in many making powders with speeds that at one time would not have been thought possible. It also acted as a catalyst in challenging some cherished myths about making Black Powder, including the value of high pressure pressing and certain charcoals. Sadly it has also had a negative impact.

Because Pyro Golf competitions focus on speed to the exclusion of other properties, speed has been given a status that perhaps it shouldnít have. Thus some now always equate fastest with best and measure so-called improvements solely in terms of improvements in speed. This doctrine has led to the rise of a new generation of the Great Green Gurus I described in the first chapter. Their powders are always the fastest on the planet -- with promises of faster yet to come -- when they have discovered the ultimate fast charcoal somewhere, somehow!

Moving On

More will be said about competition grade powders later in this chapter and in the chapter on testing. We now move on to methods and techniques for making really fast powders.

To make high speed powder one must come to terms with the following:

Milling is mandatory

Corning is recommended and is usually necessary.

Some may disagree with the above statements. However, centuries of Black Powder manufacture have shown these to be true - again and again and again.

Mandatory Milling

About ten years ago I corresponded with a fellow enthusiast who was experimenting with making Black Powder. His one memorable comment to me was: "You must ball mill. The difference is as night and day." I ball milled -- and the difference was just as he had described!

Some form of milling is mandatory if one wants to make fast Black Powder. There is just no way around this fact. Believe me, I have searched diligently for other methods that would obviate the need for milling. I have yet to find any. I have yet to find anyone who has.

I have tried the CIA method without milling. I have investigated heating up the sulfur and melting it into the charcoal. I have perused experiments done for the US military in exploring solvents that would dissolve sulfur. None of these have yielded any meaningful gains when compared with milling. So milling lives, like it or not.

Beyond hand milling with a pestle and mortar, ball milling is the method of choice for most. Thus when milling is described from now on in this chapter, ball milling is assumed unless stated otherwise.

Consider Corning

Corning should be considered as advisable rather than an option. Besides creating Black Powder grains that can be used in regulating burn speed, corning also keeps the fine particles of potassium nitrate, sulfur, and charcoal from separating from one another.

Thus corned powder is on the whole better powder. Even very fine meal powders are corned powders, as opposed to just dry mixtures of finely ground materials.

Milling Options

So far we have established that milling itself is not an option if one wants fast Black Powder. But milling is dangerous, no matter what method of milling is used. This is an unfortunate fact of life, but the dangers themselves can be reduced by choosing different options in the milling process itself. These options have been described in previous chapters. Here they are explored in more detail.

The most dangerous type of milling operation is the milling of all three components of Black Powder together. Fortunately one does not need to do this to get a very fast powder. There are ways of avoiding three-component milling without compromising performance. These are:

Single component milling

Double + single component milling

Double + double component milling

Double component milling + dissolved potassium nitrate.

Single Component Milling

Single component milling involves milling the charcoal, sulfur, and potassium nitrate separately and then mixing them together.

Before describing this process, dispelling a common myth is in order here. This concerns three component milling and what actually happens during the milling process.

A common misconception is that milling sulfur and potassium nitrate together with charcoal has the effect of pressing the other components into the charcoal. This doesnít happen because the tiny holes (or pores) in the charcoal are too small to accommodate the sulfur and potassium nitrate particles. This pressing process thus happens neither during milling nor during subsequent pressing.

So what is there to be gained by milling all three components together if this effect does not happen? Plenty, because the milling process is also a mixing process. It is actually this mixing process that is the critical factor in ensuring that the Black Powder is properly incorporated. Understanding this concept is the key to understanding how good powder can still be made without three-component milling.

Milling typically takes longer than mixing. In fact proper mixing mostly takes place when each component has been milled fine enough to ensure good intimate mixing. This is one reason why those who favor three-component milling often opt for a pre-milling process of milling the individual components before milling them together.

It makes a lot of sense to mill the components individually for a long length of time and then mix them for a shorter time period. For example one could mill each component for three hours and then mix them together by milling them together for about an hour. This process still involves three-component milling, but for a shorter time period. The shorter this time period is the less chance there is of the mill exploding.

The just-mentioned method uses the ball mill in the final mixing stage, but unfortunately creates the situation where one has had to revert to three-component milling. This three-component milling is for a shorter time period but it is still three-component milling. Are there any alternatives? Yes, there are.

Mixing can be done by sieving the three components together. The more one does this, the more intimate the mix. Alternately, one can sieve the charcoal and sulfur until they are thoroughly mixed and then sieve them together with the potassium nitrate. The mixing process can also be varied by stirring the components together with wooden spoon.

But just as ball milling beats hand grinding, doing the mixing in a ball mill beats doing it by hand.

One may opt for another solution by doing the mixing in the ball mill but without the balls. This reduces some of the dangers created by the milling media but also reduces the mixing efficiency. Reducing the efficiency means having to increase the mixing time. Increasing the mixing time increases the danger of an accident.

Other problems can occur with single component milling. Sulfur for example, can build up a static charge if milled on its own. This charge is dissipated if charcoal is added to the sulfur and both are milled together. Potassium nitrate milled on its own presents another problem. The finely milled potassium nitrate particles have a tendency of clumping together if not mixed with another substance. These problems are addressed in the following sections.

Double + Single Component Milling

This section discusses double plus single component milling. The double part is a mixture of charcoal and sulfur, while the single part is potassium nitrate. The charcoal and sulfur are milled together and then mixed with the potassium nitrate that has been milled on its own.

Note that this process only considers mixtures of charcoal and sulfur and not the other possibilities such as potassium nitrate and sulfur or potassium nitrate and charcoal. The reason for this is safety.

Before milling the charcoal with the sulfur, it is a good idea to reduce its particle sizes. A good way of doing this is to sieve the charcoal through a 50 mesh or finer sieve before mixing it with the sulfur.

This process reduces the chances of a static charge being built up on the sulfur but does not address two other important issues.

The first issue is the problem of the tendency of finely ground potassium nitrate to agglomerate. This is the process whereby the particles tend to clump together. This can be quite a serious issue, but it can be solved by mixing some charcoal with the potassium nitrate.

The second issue relates to the danger of spontaneous ignition when the finely ground potassium nitrate is added to the other components, also finely ground. I am really not sure how prevalent this danger really is. French powder makers seemed to think so. This caused them to opt for the solution described in the next section.

Double + Double Component Milling

The perceived dangers in the last section can be got around by creating two double component mixes: potassium nitrate + charcoal, and charcoal + sulfur.

Potassium nitrate with charcoal is potentially nearly as dangerous as a three-component mix if the ratios of potassium nitrate to charcoal are in critical or near critical proportions. Typically these ratios vary between 4:1 and 6:1. Mixes in this range of ratios have the potential of igniting easily and burning very efficiently.

We get around this problem by increasing the ratio of potassium nitrate to charcoal to a ratio of 15:1. Thus if we are working with Waltham Abbey proportions we take one third of the charcoal and mix this with the potassium nitrate. The remaining two thirds are mixed with the sulfur.

 

Double Component Milling + Dissolved KNO3

Another option is to combine milling with the so-called CIA method. This method differs from the others in that the potassium nitrate is not milled at all; rather it is completely dissolved in water.

This method completely eliminates the need to mill potassium nitrate and also eliminates any dry mixing of the potassium nitrate with the other components. From a safety standpoint these are two big plusses. However, there are some downsides with this method.

The first downside is that one is trading one danger for another. So itís a case of picking oneís poison. There have been some rather fierce and somewhat meaningless debates on this issue, with each side accusing the other of promoting dangerous practices. The bottom line is: all methods used to make Black Powder are dangerous, period!

Cooking up a Black Powder mixture at a temperature slightly higher than the boiling point of water can result in some painful scalding if some of the mix splashes onto oneís bare skin. A worst case scenario of the mix igniting could result in a horrible fire, with horrible burns and damage to property. An explosion using this method is highly unlikely. An explosion from dry milling and mixing is a distinct possibility. So pick your poison - fire or explosion.

The second downside is one of accuracy. Some potassium nitrate is usually lost. This means that its ratio to the other components is reduced. This reduction will usually result in some loss of speed.

The third important downside is the issue of cost. Alcohol (even cheap alcohol), is expensive. And to do a proper job, lots of alcohol is needed.

Other negatives are that alcohol precipitation is tedious, time consuming, and messy.

The so-called CIA method is described in the chapter entitled The CIA Connection, together with my suggestions for optimizing this technique.

Pressing and Corning

With the exception of the last-mentioned method that involves dissolving the potassium nitrate in water, all the powders are pressed with a minimal amount of dampening. Some dampening is needed to ensure proper pressing into pucks or pellets.

Some have suggested using just alcohol for this process instead of water or an alcohol/water mix. I donít recommend this practice because potassium nitrate in insoluble in alcohol. A small amount of water dissolves some of the fine potassium nitrate powder, causing it to bind together with the other ingredients. This is very important for the formation of viable Black Powder grains. If this water is kept to an absolute minimum then one doesnít have to worry about problems such as leaching out or the formation of large crystals.

To practically implement this dampening process one should add water in very small increments and mix the powder with a wooden spoon until it just starts clumping together. A good way of doing this is to place the water in a hand-held spray bottle like those used to hold window cleaner, and lightly spray the surface of the mix while mixing.

The dampened mix is then pressed into pucks or pellets using any of the techniques described in previous chapters. Some techniques will probably yield better results than others.

The resulting pucks or pellets are then dried. I have dried mine for just over a day during the hot summer months. Others have reported drying times of a week or longer. There are no hard and fast rules here. Each person needs to find out what is best for them in their particular circumstances.

The thoroughly dried pucks or pellets are corned using a variety of techniques. Some have gone to the trouble of acquiring or making machines similar to those used by commercial manufacturers, but most havenít. So crude and simple still rules the day here.

My preferred method is to place individual pucks between sheets of paper on a hard flat surface and run a pastry rolling pin over them, the same way that one rolls out pastry. I apply enough pressure to initially crack the pucks, causing them to crumble. I then repeat the process until the whole puck is reduced to small grains.

Others have placed their pucks or pellets on a hard surface under layers of plastic sheeting and struck them with a mallet. Another method is to place the puck or pellet in a press and slowly apply pressure until it crumbles. Note that this pressure should be applied slowly in a controlled manner. Too fast an application of pressure could result in the press acting in a way similar to an impact tester, igniting the powder in the process.

The resulting grains are then passed through sieves to give the required sizes.

Beyond Corning

Black Powder that has gone through the corning process is ready to be used as is. No further processing is necessary. However, some improvements in performance can be gained by a process that is often referred to as polishing.

Polishing the powder grains rounds off their rough edges and yields a better consistency in grain shape. It also helps to pre-empt some breaking up of individual grains during transport and handling. This in turn may relate to better performance, depending on the application. Sporting powders are usually polished.

The polishing process can be carried out by simply tumbling the grains in a ball mill without the balls. The grains are tumbled until the desired finish is reached and then sieved to remove the fines.

Sporting powders usually have a small amount of graphite added during the polishing process. The graphite assists in making the powder flow better when loading and offers some protection against moisture. Such powders are known as glazed powders and are denoted with a g suffix, e.g. 2Fg.

Glazed powders are more difficult to ignite than their unglazed counterparts, and thus effectively have a slower burning rate. Glazed powder grain sizes are different to those used in unglazed powders. Thus a 2Fg powder is much smaller in size than a 2Fa powder. The same holds true for the other sizes such as 3Fg, 4Fg, etc.

Competition Grade Black Powder Revisited

Having explored ways and means of making very fast powders that could comfortably perform as competition grade Black Powder, it is worth paying attention to the competition itself.

The Pyro Golf competition originated with a few Black Powder enthusiasts comparing different powders made with different charcoals. This stimulated more interest in homemade Black Powders. A catalyst in this was the discovery that making Black Powders that performed as well as (or even better than) commercial powders such as GOEX. So Pyro Golf inspired a renewed interest in homemade powders.

The original Pyro Golf tests used 4 grams of powder per test. As the new generation of amateur powder makers improved their powders, 4 grams was found to be too much. This amount was reduced to 3.5 grams and finally to 2. From a competition standpoint, 2 grams of Black Powder is now considered the rule. Flight times are thus related to 2 grams, rather than the larger amounts previously used. This is important when comparing older results with their more recent counterparts.

Other rules that appear to be unchanged at the time of writing this relate to density and grain size. Both of these can have a significant impact on performance.

As a general rule, the lower the density the faster the powder. This conflicts with the once-cherished belief that high density powders burned faster. The inverse relationship between density and speed has been confirmed by many different tests done by different persons, at different times, under different conditions. The following tables give snapshots of some of these tests:

 

Powder Type

Average Flight Times (in seconds)

 

High Density

Low Density

JF

11.90

13.91

TD

11.47

13.29

DM

8.19

8.86

 

The above data shows a flight time variation of between 8 and 17 percent, the variation being defined as the difference between low density and high density powders.

 

Powder Type

Average Muzzle Velocity (feet/second)

 

High Density

Low Density

Silver Maple

330

360

Aspen

360

380

 

The above data shows a muzzle velocity variation of between 5 and 9 percent, the variation being defined as the difference between low density and high density powders.

Powder Type

Average Peak Pressure (psi)

 

High Density

Low Density

Silver Maple

390

560

Aspen

460

600

The above data shows a peak pressure variation of between 30 and 44 percent, the variation being defined as the difference between low density and high density powders.

 

Powder Type

Average Muzzle Velocity (feet/second)

 

2F

4F

GOEX

200

250

NLC

220

420

The above data shows a muzzle velocity variation of between 25 and 91 percent, the variation being defined as the difference between large grain and small grain powders.

 

Powder Type

Average Peak Pressure (psi)

 

2F

4F

GOEX

84

130

NLC

170

730

The above data shows a peak pressure variation of between 55 and 429 percent, the variation being defined as the difference between large grain and small grain powders.

Powder Type

Average Flight Times (in seconds)

 

2Fa

2Fg

3Fg

4Fg

GOEX

10.09

12.59

12.66

12.87

The above set of data is interesting in that there is a 25 percent variation between the 2Fa and 2Fg powders but only a 27.5 percent difference between the 2Fa and 4Fg powders. This suggests that the influence of grain size drops dramatically after a certain point.

The above test snapshots demonstrate that significant differences in muzzle velocity, peak pressure, and flight time can occur with changes in density and grain size. This means that these variables need to be taken into account when comparing different powders. So where does this leave so-called competition grade powders? At the time of writing this it leaves them wanting.

Comparing two powders with significant differences in density is like comparing apples and oranges. The same can be said about comparing powders with different average grain sizes. And here I am not merely referring to different grades such as 2Fa and 4Fa. Differences can occur even within the grade size itself. The following data should help to illustrate this point:

 

 

Grade

Largest Grains (inches)

Smallest Grains (inches)

Ratio (largest/smallest)

Fa

0.3125

0.157

1.99:1

2Fa

0.187

0.0661

2.83:1

3Fa

0.0787

0.0469

1.68:1

4Fa

0.0661

0.0331

2.00:1

Pyro Golf

0.0937

0.0661

1.42:1

 

The above data shows ratios varying from 2.83:1 to 1.42:1. In fairness to the Pyro Golf competition ratios, these yield a closer grain size than any of the others shown. However, a ratio of 1.42:1 can be improved upon to yield more meaningful results.

An improved ratio of about 1.19:1 can be realized by using two adjacent standard sieve sizes in the ranges of No.8 (0.0937 inches) to No.20 (0.0331 inches).

GOEX Black Powder Revisited

It has become common practice to compare homemade powders to GOEX, with oft-repeated claim of being faster than GOEX. At one time such claims were met with a certain amount of skepticism. This is no longer the case. Many of such claims are valid.

Even laying aside fudge factors such as tweaking densities and grain sizes to give faster speeds than GOEX, many claims of faster powders are still legitimate. Why is GOEX slower? And for that matter, why are other commercial powders slower?

Part of the answer to these questions is that commercial manufacturers donít aim for the fastest powders on the planet. They have other important objectives such as consistency from batch to batch and powders that have good ballistic properties.

I recently spoke to a representative from GOEX who has been in the Black Powder making business for close on forty years. His father before him was also a Black Powder man with long years of service in the industry. He commented on the fact that faster is not necessarily better. He illustrated this with examples from sporting grade powders that compromised accuracy when made to perform slightly faster than normal. And no, one cannot always just reduce the amount of powder if the powder burns faster. The science of ballistics is a bit more complex than that.

Could GOEX make faster powders? They certainly could by perhaps using different charcoals and reducing the densities of their finished product. They could also be creative in changing their grain sizing. But to what end?

Such an end result could be faster powders that compromise other characteristics such as consistency from batch to batch, resistance to moisture absorption, and resistance to crumbling when handled and transported. Such considerations may not be important to an amateur experimenter, but are very important to commercial manufacturers and many of their customers.

So no, there is no conspiracy among commercial manufacturers to keep the speed of their powders down, thus forcing helpless consumers into buying more of the stuff.

Conclusion

This chapter has described ways and means of making fast Black Powder. It has also shown that such powders can meet or exceed the speeds of those found in commercial powders. And it has shown that making fast Black Powder is a relatively simple process.

This last point may have a peculiar significance to those who have been hoodwinked into thinking that the secrets of fast Black Powder belong to those who have spent many years in perfecting the art. Black Powder making is not a black art. Conversely it is not rocket science. Its secrets are not closely guarded by a small group of luminaries. It can be made by anyone who is willing to apply themselves in a disciplined and common sense way.