Types of Smokeless Powder
Date: Jan 20 2005
There are three basic types of smokeless powder: flake, extruded and ball.
The names refer to the shapes of the individual particles, which are called granules. (Granule may seem like an odd word. It’s used instead of grain because in the avoirdupois measuring system commonly used by Americans, a grain is a unit of weight, 1/7000th of a pound.) The shape of each granule affects how quickly the powder burns, but this is also affected by the chemical makeup of the powder.
Flake powder looks like little flakes of black paper. The flattened granules provide more surface area per volume than those of ball or extruded powders, so flake powders are normally fast-burning—hence most useful in shotshells, lower pressure handgun cartridges, and reduced rifle loads. Alliant probably markets more flake powders than any other company today, including such old and popular brands as Red Dot and Unique.
The easily-ignited flakes don’t require a magnum primer, in fact they may work better with the mildest primer available. They’re a particularly good choice for shotshells used in cold-weather hunting; a good rule here is to use the fastest-burning flake powder suitable for the load.
Flake powders were notorious for decades for incomplete burning in low-pressure use, particularly in shotgun loads, which average around 10,000 pounds per square inch (psi). Newer versions of the old powders (such as Unique) tend to burn much more cleanly, however.
Extruded powders are formed by forcing the wet powder compound through round holes. The extrusions are then cut into little cylinders, resembling tiny logs—the reason extruded powders are often called log powders by handloaders.
The cylindrical shape of the granules offers far less surface area to each granule than the wide, flat sides of flake powders, so extruded powders tend to be slower burning. The larger the log, the slower it burns (just as in a wood stove) so the very slowest extruded powders have the largest granules. Many of the most popular slow-burning rifle powders are extruded, including IMR4350, Hodgdon H4831, and Alliant Reloder 22, but many fasterburning extruded powders are very popular, especially the IMR and Hodgdon versions of 4227 and 4895.
The biggest advantage of extruded powder is that the log-shape plays a large role in controlling burning rate, so not many additives (especially coatings) have to be used. The fewer the additives, the less residue left in the barrel.
The biggest disadvantage of the slower extruded powders is that the large granules don’t measure or flow as consistently in a mechanical powder measure. Easier measuring is the big reason for Hodgdon’s line of short cut extruded powders, with granules about half as long as traditional extruded powders. However, the smaller-granuled extruded powders, especially tiny-grained numbers like IMR4227, measure very accurately and easily.
Ball powder granules look like little balls, though often they’re not perfectly round, and sometimes are deliberately flattened to increase burning rate. Ball was the last type of smokeless invented, essentially designed for mass ammunition manufacture. Ball is cheaper to make than flake or extruded powders, and the little balls flow accurately through a powder measure.
Ball powders can be made in about any burning rate from superfast to very slow, by varying the size of the granules and adding a deterrent coating to their surface, slowing initial ignition. Such coatings, however, by their very definition don’t burn well. Consequently older ball powders tended to leave a coat of fine, dark fouling in the bore, requiring frequent cleaning to retain the finest accuracy. Newer ball powders such as the Ramshot line, however, use deterrents that are mostly consumed later in the burn, leaving bores about as clean as when using extruded powders.
Many newer powders are also far less sensitive to temperature than older powders, especially cold. With older powders it was common for loads to lose 5% or even 10% of their velocity from 70 degrees F. to zero degrees, which often affected point of impact. Among the new, cold-tolerant powders are Hodgdon’s Extreme line, and the Ramshot line of rifle powders. Despite their tolerance to cold, however, pressures and velocities still tend to rise at temperatures above 70 F., though not as quickly as with older powders.