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Different Grades of Black Powder
Posted by Kevin Rath on 03 December 2011 07:09 PM
Black powder grades

Black powder types are purchased and described by "grades".
The grades carry numbers or designations to declare their granule sizes, and their relative speeds of burning.
Those numbers are familiar to pyrotechnicians - the famous 'F' numbers.

Powders come in two broad basic grades, "a" grade, or blasting powder, and "g" grade, or "sporting" (shooter's) powder.

The more "F"s in a number, the smaller the granule size, and thus, the faster the powder will burn.
So, FFa powder is slower, with a larger granule size than FFFa, and FFFg is faster than Fg.
The primary difference between "a" and "g" grades is processing. Both powders begin as milled "meal" powder.
The potassium nitrate, charcoal and sulfur are milled into an extremely fine powder.
This milling process takes many hours and is usually 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 by hydraulic press.
The cake is dried, and crushed into grains. Both types are then screened to remove fines, and to grade the grain sizes. Subsequent polishing of the powders may be done in a tumbler.
Blasting "a" type powders are not usually tumbled.
If they are 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 base formula is the same. The graphite is not part of the basic Black Powder formula. The graphite does act as a burn rate modifier, slowing the burn rate slightly.
But primarily, the graphite serves as a surface lubricant to make the powder flow more easily when loading guns.
It also serves the cosmetic purpose of making the powder shiny and pretty.
The grain sizes are different for sporting and blasting Black Powder. Note, as shown in the tables below, that it is conventional to express "g" powder types with multiple f's followed by a lower-case "g".
While "a" grade powders wear a number before one "f", and a capital "A".
So, "3 F g" powder is written as "FFFg", while "3 F a" powder is written as "3FA".
This convention is thought to have been instituted so that less confusion would exist between powder types.
For a given number of F's, "a" grade powder is coarser and slower-burning than "g" grades, not with standing the graphite polish on the "g" types.

Sporting Grade Black Powder -- "g" type powders.

Powder Grade	Pass Screen	Holding	Stays On	   Passing

Whaling	        32/64" mesh	  3%	          4 mesh	     12%
Lifesaving             6 mesh             3%         12 mesh        12%
Cannon                 6 mesh            3%          12 mesh        12%
Saluting              10 mesh            3%          20 mesh        12%
Fg                      12 mesh            3%          16 mesh        12%
FFg                    16 mesh            3%          30 mesh        12%
FFFg                  20 mesh            3%           50 mesh        12%
FFFFg                40 mesh             3%         100 mesh        12%
FFFFFg                         (no longer manufactured by Goex)

____________________________________________________________________________

"A" Blasting Powder - Used mostly by pyrotechnicians and for some specialized quarry work.

Powder Grade	Pass Screen	Holding	Stays On	Passing

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

** 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, that the blasting powder is much coarser. Reference: AMCP 706-175 Engineering Design Handbook - Explosives Series - Solid Propellants Part One.
Thanks to Bill Nelson and Murr Rhame for collating most of this data. If you ignore the "f" numbers, for a given measured grain size, the blasting powder burns faster than the graphite-inhibited sporting powder;
That's partly because of the inhibiting action of the graphite, and partly because of the geometry of the grains. Blasting powder is less dense because the grains are more irregularly shaped; they take up more volume for a given weight of powder.
Blasting powder grains also have a lot of rough edges. Rough edges both inhibit packing of grains, and offer lots of easy-to-ignite sites on each grain.
The combination of more air space between grains, and the rougher surfaces of the grains promotes faster burning.
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