Manufacturing Process

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Black powder makers relied on fine grinding of the components to ensure that they were mixed thoroughly. However, military use of propellant-grade black powder gave rise to a serious problem; dry components could separate during transport over rough roads. This caused a degradation of the propellant’s power. A short-term cure was to transport the components separately to the battlefield and mix them just before loading. The hazards of a propellant blending operation close to an active line of cannon are easily imagined.

The solution for the separation of the components of this mechanical mixture proved to be the only significant improvement to black powder in its long history. Small amounts of water were added during the milling and grinding operations. Potassium nitrate is soluble in water; adding a small amount of water causes it to become slightly sticky. Then the potassium nitrate can act as a binder to hold the two insoluble components in close contact. The presence of moisture also reduces dust. This largely mitigates the major hazard of blending and grinding as long as an adequate moisture level is maintained. This wetting process is called corning, and the resulting product was called corned powder.

The corned powder is pressed into cakes and allowed to dry. After drying, the cake is broken into granules. All granules contain uniform proportions of the components and maintain those proportions until consumed. Corned powders proved to be much more powerful than the dry mixture, largely due to the incorporation of ingredients. Some cannon that were suitable for the weaker dry-blended powders proved inadequate for corned powder. The improvement in propellant forced an improvement in gun metallurgy.

The granulation process serves another useful purpose; some control of the rate of energy release is afforded by sizing the granules. The granulated pieces are passed through sieves to sort them by size. Larger granules release energy at a slower rate than fine granules. This characteristic means the user can select from several grades to obtain the best velocity from a black powder firearm. Large-bore devices, such as cannon, use coarse granules (up to several millimeters average size). Small-bore devices, such as shoulder arms, use much finer material.

In the United States, sporting black powder is sold by size as indicated by a coding system with the letter “F.”

For example:

1F: coarse, for .69 to .75 caliber muskets
2F: medium, for .45 to .58 caliber rifles and muskets
3F: fine, for .31 to .45 caliber rifles and most handguns
4F: extra-fine, only for priming flintlock arms

Note:

Some have suggested that black powder propels a projectile by a weak but high-order detonation, unlike modern propellants that burn to push the bullet out of the barrel with a progressive increase in pressure. The author has participated in research where black powder was loaded in a cartridge [.45-.70 government cartridge with a 500-grain (32.4 gram) bullet] and then test fired in a modern piezoelectric ballistic pressure system.

That research showed the following:

Black powder produces time-pressure curves that are remarkably similar to modern propellants, indicating progressive burning and a measured release of energy over time.
Black powder in finer granulations produced higher pressures than equal quantities of coarser black powder, indicating the burning rate is controllable by granulation.
Black powder peak pressures were as high as 21,000 psi, and roughly equal to modern factory ammunition for this cartridge.

With the improvements of corning and grading, black powder remained largely unchanged until military and sporting arms transitioned to modern propellants at the beginning of the twentieth century.

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