It is critical that a pyrotechnic learns to make quality black powder. Commercial muzzle loading BP can be bought for ~$20/lb in most areas, and is usually suitable for use in fireworks. However, BP made properly at home can far exceed the burn rate of commercial, and only costs ~$1/lb if chemicals are bought fairly. At that price difference, buying the equipment pays itself off very quickly.
Digital Scale – As with all compositions, an accurate scale is the most important tool. With only a scale, if your chemicals are already in fine powder form it will at least be possible to make hand mixed BP called greenmix. The burn rate of greenmix is rather slow, too slow to break shells, but it may lift them if an excess amount is used. Without a scale, it will be impossible to make consistent BP at all, or any other composition for that matter.
A good pyrotechnic scale should be accurate to at least 0.1 gram, and a load capacity of at least 500 grams. I use and much prefer digital. These can be bought many places, both online and are also commonly sold at health stores. The intended use for them is to measure jewelry or nutrition food products.
Ball Mill – This is the most expensive tool needed for making black powder, but it is well worth it. Ball mills are extremely useful not only for BP, but for all BP based compositions and the individual chemicals of many others. There are many stars that will not function at all if some or all of the composition is not first ball milled. Other methods of grinding such as by hand with a mortar and pestle are not capable of achieving what is needed for good BP.
A good ball mill can be bought for well under $100, though even that is often more than a starving pyrotechnic can spare. As a result, many have resorted to building their own mill. Rock tumblers have also been used to some success, but they require much longer run times to achieve the same result as a proper mill. Whether you decide to go the route of buying or building a mill, you will need media to use in it. Lead is by far the most common since it is readily available in 50 caliber muzzle loader balls, is heavy, and is non-sparking. Brass is the other semi common media because of similar properties. One of these two medias is a must. Using media such as glass marbles or the like will result in disaster. Stick with what is known to be safe. Mills can be bought at a variety of pyrotechnic suppliers online.
Screen or Pasta Strainer – This is merely for granulating the BP once it has been milled. Any large mesh screen or pasta strainer will do fine.
Getting To It:
The first step of making good black powder is found in the chemicals used:
Potassium nitrate is usually quite pure from any supplier and very suitable for BP. Sulfur, if bought from a pyrotechnic supplier is also usually pure, but if bought as the garden store variety contains about %10 clay. When used in BP that evens out to be a %1 clay addition to the mix, meaning the BP will still preform fine for just about any purpose, but will not be quite as fast as it could be.
Charcoal is the real deciding factor. The wood the charcoal comes from plays a large part in the burn rate of BP. Some woods that are particularly good for fast black powder include: Willow, Buckthorn, Balsa, and I have also had great success with White Pine. Other charcoals made from mixed hardwoods as you would buy from most pyro suppliers will work suitably well for BP, but as with sulfur, not as well as they could.
The process used for making black powder is rather simple once all the equipment and chemicals are purchased. The proper ratio of each chemical is weighed out and placed into a ball mill jar with 50 cal lead ball or brass media. It is not at all likely that the BP will combust in the mill, but as a safety precaution always let it run outdoors or in a detached structure from any occupied area. For best milling the jar should be filled halfway with the BP composition, though if it is slightly over filled it will only take more time to properly mill. The milling time is dependent on many factors, but as a rule of thumb: More milling time = faster BP. Between 8-10 hours is as long as needed.
Eventually, the Bp will begin to stick to the walls of the mill if left in long enough. This is fine, but it is not necessary to wait quite that long for your result to be adequately fast. If the Bp sticks to the walls before 8 hours of milling has passed, it is possible that one of your chemicals (probably potassium nitrate) has to much moisture in it. This can be solved by placing your nitrate on a tray in the sun to dry before using it for your next batch of BP.
When the milling is completed, screen the media out of the composition by dumping the contents of the milling jar onto a heavy screen or pasta strainer, allowing the composition to fall through onto newspaper or into a large bowl. Place the media back in the jar for later use milling BP type compositions.
The BP now made is in the form of what is called meal powder, and is perfect for coating rice hulls for break. However, for lift the BP must be in granulated form. To achieve this, begin to dampen the BP with water in a bowl until it forms a solid clay mass. As water is added, mix in a tablespoon of liquid laundry starch per 100 grams of BP. Be careful to not get the BP so wet that it turns to a soup. It should be a fairly dry clay.
Now force the composition through the strainer or screen and it will come out granulated on the other side. It should be granulated upon sturdy kraft paper or another surface that will not rip when damp. Newspaper is too flimsy for this. When all the BP is granulated, allow it to sit outside to dry. When the paper it is sitting on is no longer soft from the moisture and becomes crisp, the BP is dry and ready for use.