Gunpowder, also known as black powder, is a simple mixture of sulfur, charcoal and potassium nitrate that has been used as a propellant in firearms and explosives for centuries. When ignited, the components rapidly oxidize and produce volumes of hot solids and gases that can be used to propel a projectile from a gun barrel. One of the key specifications of black powder is the grain size, which refers to the physical dimensions of each granule of powder.
What is grain size?
The grain size indicates the approximate diameter of each granule of powder, measured in fractions of an inch. For example, Fg (fine grain) powder has granules that measure approximately 0.020 inches in diameter. Coarser powders are designated as FFFg (0.040 inches), FFFg (0.060 inches) and FFFFg (0.080 inches). The smallest permissible grain size of black powder allowed for commercial sale in the United States is Fg.
Grain size affects the burn rate of the powder. Finer grains have more surface area relative to their volume, which allows for faster burning. Coarser grains burn more slowly due to their smaller surface-to-volume ratio. Different applications call for different burn rates. For example, fast-burning powder is desirable for use in some firearms, while slower burning powder is recommended for cannon firing.
How many grains in a pound?
Black powder is measured by weight and the fundamental unit is the grain. A grain is defined as exactly 1/7000th of one pound, or approximately 64.79 milligrams. So there are exactly 7000 grains in one pound of black powder.
This relationship makes conversions easy. For example:
- 1 ounce = 437.5 grains
- 1 pound = 7000 grains
- 1 kilogram = 15,432 grains
While modern smokeless powders are measured in weight units like grams and pounds, black powder stick to the traditional grain measurement due to its long history of use. The grain system provides an easy method for precisely measuring small quantities of powder for reloading ammunition.
Does grain size affect the grain count?
While the burn rate and ballistics are affected by grain size, the number of grains in a pound is the same regardless of the diameter of each granule. A pound of Fg powder contains exactly 7000 grains, just like a pound of FFFg or other sizes.
This is because the definition of a grain is the same, even though the physical dimensions of the powder grains vary. Think of it like counting sand granules – a pound of fine sand will have just as many individual grains as a pound of coarse sand, even though the coarse grains are much bigger.
So whether the powder is fine or extra coarse, a pound is 7000 grains.
Grains per pound examples
Here are some examples to illustrate the number of grains in various quantities of black powder:
- 1 ounce of black powder = 437.5 grains
- 1/4 pound of powder = 1750 grains
- 1/2 pound = 3500 grains
- 1 pound = 7000 grains
- 5 pounds = 35,000 grains
- 20 pounds = 140,000 grains
As you can see, the relationship holds true regardless of the quantity of powder. So if you know the weight in pounds, you can easily determine the number of grains by multiplying by 7000.
Usage examples
Knowing the number of grains in your powder charge is critical for accurately reloading ammunition. Here are some examples:
- A typical black powder rifle load uses around 100 grains of FFFg powder.
- Black powder revolvers generally use charges in the range of 10-20 grains of FFFg per chamber.
- A 10 gauge shotgun shell may be loaded with around 350 grains of Fg powder.
- Flintlock muskets often use charges of up to 150 grains of FFFg powder.
These examples demonstrate how the grain measurement allows efficient use of black powder. Reloaders can precisely measure powder quantities without weighing each charge individually.
Computing other quantities
Knowing the relationship of 7000 grains per pound allows some useful computations. For example:
- 1 grain weighs 0.0022857 ounces (1/7000 lb).
- In metric units, 1 grain is 64.79 milligrams (1/15,432 g).
- There are 454 grams (1 lb) per 7000 grains, so 1 grain equals 0.0648 grams.
With this information you can interconvert between grain and ounce or gram measurements when working with black powder.
Effects of powder compression
One factor that can alter grain density is compression. When black powder is compressed under high pressures, the granules are packed more tightly together with less air gaps between them. This increases the bulk density.
For example, compressing 20 pounds of loose FFFg powder into a volume of one cubic foot could increase its density from around 25 pounds per cubic foot to 35 pounds per cubic foot. This compressing action does not actually change the number of grains, but it does increase the weight for a given volume compared to loose powder.
Compressed powder burns at a faster rate due to the increased density. Granule shape also affects the degree of compression – flattened grains can be stacked tighter than round ones.
Fun facts
- At 64.79 milligrams per grain, a pound of black powder contains enough granules to weigh over 450 grams.
- Duplicating a pound of powder by manually counting out 7000 individual grains would take around 5-6 hours!
- Laying 7000 grains end-to-end would span approximately 90 feet in length.
- 7000 grains is approximately one tablespoon – measuring powder by volume is very imprecise.
Conclusion
In summary, a pound of black powder contains exactly 7000 grains, regardless of powder type or granule size. This useful relationship allows easy conversions between pounds and grains for precise powder measurements. Understanding the number of grains in a pound of gunpowder is key for reloaders and shooters using black powder firearms.
