The shape and size of an individual grain of powder has a large impact on how it burns, meters, and fills the case. Because of this there are many different shapes or geometries that are found in the wide array of powder that is available to manufacturers and Consumers. Not all geometries are created equal, and while they may perform very similar in lab or in a hobby reloading set up, they can cause significant challenges in manufacturing.
Generally the geometry of a powder grain can be broken up into three basic shapes.
Flake Powders
Flake powders are flat, and may be cylindrical or are cut into squares. Typically flake powders are used in very fast burning applications. Flake powders are very common in pistols and shotguns, but are not found in the medium to slow burning powders. It is also common that many flake powders have a dye applied to a few of the powder grains that can be useful in identifying the powder. For example Alliant Blue Dot powder has flakes which are colored blue.
Flake powders have a neutral burn profile. This means as the individual grains burn they surface area remains fairly constant. The gas generation is also fairly steady, these powders tend to burn quickly and the overall burn time is short. Making these good candidates for pistols which have short barrels, or shot guns which have large bores and need lots of gas quickly to fill the space. Flake powders are also typically not ideal for use above 35kpsi.
Generally flake powders meter well in commercial loaders. Not as well as ball powders, as they can clump but this is rare. Flake powders tend to be “Fluffy” and can occupy more space then their counter parts. This make flake powders a good choice when loading cartridges that were originally designed for black powder. Examples would include 38 Special and 45 Colt.
Ball Powders
Ball powders are characterized by having a spherical resemblance. During manufacture the powder may begin as a sphere and be flattened out to create a “Flatten Ball” looking similar to a very fine flake powder. They may also be haploid, oblong or tear drop in shape.
Ball powders are unique the sense they have a wide range of shapes. Purely spherical powders have a regressive burn. Which means the surface area decreases the more the grain burns. This mean the powder grain generates a lot of gas when it initially ignites but it slows down as it proceeds to get smaller and smaller. There are few powders that are truly spherical. There are many shapes that fall under the “Ball” powder category. Undoubtedly these different geometries create unique burn profiles that are not easily categorized by geometry. For this reason ball powders are found in fast burning pistol and shotgun loads, to slow burning 20mm Cannon powders.
Ball powders generally meter very well in commercial loading equipment. However they can sometimes be so fine that they get into nooks and crannies where other powders can’t. This can cause premature wear of powder metering parts. This may be remedied by the installation of wipes, or tooling that has tighter tolerances then the OEM tooling.
Extruded Powders
Extruded powders are characterized by grains shaped as”rods”. The grains may be pierced or perforated in the center to create tubes. The lengths and thickness very greatly, though they are typically at least as long as they are thick.
Extruded powders can cause issues with loading machines such as the Camdex 2300 or the Setpoint Loaders, especially when there is a large charge that needs to be metered in a small diameter case neck. An example of this would be trying to meter Reloder 26 into 6.5 Creedmoor. This is an excellent temperature stable powder and performs well in the 6.5 Creedmoor, however it is difficult to meter on many automated loading machines.
Extruded powders are similar to Spherical powders and have a regressive burn profile. The surface area decreases proportional to the fraction of grain burned. Similar to spherical powders there may be some variation in geometry that can help change the over all burn profile.
For example tubes or perforated grains have a more progressive burn profile. Meaning that as the grain burns the surface area increases. The increase in surface area increases the rate of gas generation. This is ideal for rifles, where you want to sustain a higher pressure over a long duration.
Extruded powders are typically relegated to medium to slow burning rifle powders. Some powders may be appropriate for use in a magnum pistol loads, but few if any extruded powders are found in shotgun loads.
Blended Powders
Blended powders may have several different powder geometries blended together as one. The example provided in the photo below has flake powder mixed with flattened ball grains.
It is very likely that there are many powders on the market are a blend of a few different powders. Powder manufacturers will regularly blend different lots of powders in order to achieve one lot that has the desired burn characteristics. Generally this is not obvious to the consumer.
With CFE BLK it is obvious there are a few different grain geometries that are present. Large flakes mixed with grains that appear to have markedly less graphite coating. There are undoubtedly more examples of this on the market that I have not yet come across.
Should be go without saying that these blended powders will have unique burn profiles that are different then just a typical ball or flake powder. This goes the same for meter-ability in loading equipment. Though with the majority of the powder being ball, there is little doubt it will meter like a ball propellant.
Chemical Additives
The shape of the grain will help determine how easily it will ignite, how well it meters, and how it burns. It is not the whole story. There are many chemical additives applied to the grains that will slow down the burn to make the powders burn more progressively. These work with the single or double based chemistry to create a burn that is truly unique to that formulation. Below are a few examples of chemical additives and how they affect the propellant.
Dinitrotoluene, a precursor to TNT, was often used as a deterrent to slow the burn rate. Due to REACH, this chemical is being phased out for less cancer causing chemicals.
Graphite is a popular additive that lubricates the grain to help it meter and to dispel static electricity. Powders with lots of graphite are apparent as they really make the muzzle dirty.
Bismuth and Tin compounds are added to the powders to reduce or prevent copper fouling in the bore.
Potassium Nitrate and Potassium sulfate are additives that are used to reduce the muzzle flash.
Identifying Powders Based on Powder Characteristics
Powders manufacturers can often be identified by examining the grain geometry. If someone wants to reverse engineer a load, viewing the powder under a microscope will go along away to narrowing down the possible powders. Propellant manufactures typically offer one or two geometries of small arms propellant.
If it is a Ball or Spherical Propellant, then St. Marks, PB Clermont, or Lovex/Explosia, are all good candidates for the origin of that propellant.
Extruded Propellants are offered by General Dynamics Valley Field plant, ADI in Australia, and Bofors in Europe.
Flake powders may be from New River Energetics (Alliant), but also may be Vectan powders.
Looking at examples from each manufacturer and comparing it to sample propellant will narrow it down to one or two possible manufacturers. From there, the use of a burn rate chart and load manuals can narrow down the range of powders that are appropriate for that particular load. Doing this you can typically narrow down the powder to two or three possible powders. Testing these powders will undoubtedly confirm which powder is being used.
Remember some powder blends are only sold to particular customers. While you might know that St. Marks powders makes the powder, they might not be able to supply it to you if its only being sold to Hogdgon. If you aren’t an manufacturer you are limited in the powders you will be able to get to those sold over the counter. With that said the range of powders sold to the consumer is truly impressive and even if you cannot get the exact powder, you will likely be able to get a powder that is very close.