Black Powder Types and Grain Sizes

The primary difference between "FA" and "Fg" type powders is processing. Both powders begin as milled "meal" powder. The potassium nitrate, charcoal and sulfur are milled together into an extremely fine powder. This milling process takes many hours and is done by remotely operated equipment due to the inherent danger of the process. The meal powder is consolidated under high pressure into a "mill cake" or "press cake" of solid Black Powder. Powerful hydraulic presses are typically used to press the meal powder into solid cakes. The mill cake is then dried and crushed into grains. The crushing process is called corning. Both types of powder are screened to remove fines and to separate the different grain sizes.

Blasting "A" type powders are not usually tumbled. If blasting powder is tumbled, it is just for a short time to knock off any sharp and long projections. Sporting "g" type powders are tumbled with a tiny amount of graphite to polish the grains. The Black Powder formula is the same. The graphite is not part of the basic Black Powder formula. Graphite does act as a burn rate modifier. The trace of graphite slows the burn rate slightly. Grain sizes are different for sporting and blasting powders.

The "A" type powder is a blasting powder, and is used mostly by pyrotechnicians and for some specialized quarry work.

Sporting Grade Black Powder
Whaling 32/64" mesh 3% held 4 mesh 12% pass
Life Saving 6 mesh 3% held 12 mesh 12% pass
Cannon 6 mesh 3% held 12 mesh 12% pass
Saluting 10 mesh 3% held 20 mesh 12% pass
Fg 12 mesh 3% held 16 mesh 12% pass
FFg 16 mesh 3% held 30 mesh 12% pass
FFFg 20 mesh 3% held 50 mesh 12% pass
FFFFg 40 mesh 3% held 100 mesh 12% pass
FFFFFg No Longer Manufactured by Goex

Blasting Grade Black Powder
FA 20/64" mesh 3% held 5 mesh 12% pass
2FA 4 mesh 3% held 12 mesh 12% pass
3FA 10 mesh 3% held 16 mesh 12% pass
4FA 12 mesh 3% held 20 mesh 12% pass
5FA 20 mesh 3% held 50 mesh 12% pass
6FA 30 mesh 3% held 50 mesh 12% pass
7FA 40 mesh 3% held 100 mesh 12% pass
Meal D 40 mesh 3% held
Meal F 100 mesh 3% held
Meal XF 140 mesh 3% held

*** Shows maximum percentages held or passed by the sizing screens. Except where noted in inches, the screen sizes are in wires per inch. The higher the mesh number the smaller the opening size.

*** Note that, for any given number of "F"s, the blasting powder is much coarser.

For a given grain size, blasting powder burns faster than sporting powder. Blasting powder is less dense due to the more irregular shapes occupying more volume for a given weight of powder. Due to the rough shapes, blasting powder also has a larger surface area for a given grain size.

Blasting powder has no added graphite to slow the reaction rate. Lower density, greater surface area, and the absence of graphite coating promote faster burning of blasting powders when compared to sporting powders of the same grain size.

Blasting powder has a wider range of granule sizes for a given grade of powder. The grading screen pairs used for blasting powder are not as close to the same mesh opening sizes as the sizing screens used for sporting powder.

Blasting powder always includes a fair quantity of fines (dust) in the mixture. The fines tend to settle to the bottom of the container. This dust burns much faster than the larger grains.

The grains of sporting powder are much more uniform in shape than blasting powder. Sporting powder grains are nearly spherical like well worn river rocks. Blasting powder grains have very rough shapes like freshly crushed stone.

Due to the uniformity of size and relatively smooth grain shapes, sporting BP lends itself to fairly accurate measurement by volume. Blasting powder must be weighed if accurate quantity measurement is required.

The graphite coating on sporting BP is quite porous. Even though the graphite coating can make water bead somewhat like a waxed surface on an automobile, the coating does not moisture-proof sporting BP. Water vapor can penetrate the graphite coating.

Reference: AMCP 706-175 Engineering Design Handbook - Explosives Series - Solid Propellants Part One.
Thanks to Bill Nelson for providing most of this data.
Reprinted from the Pyrotechnics Mailing List -
Date: 10/02/95
Author: Murr Rhame

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