Welcome Spark Shooter.
A very good question. You are going to get several short answers, but I will try to give you a somewhat long answer as perceived by many of us old timers, and taught to us by Bill Knight, better know as the "Mad Monk".
"Sporting Grade powder" typically relates to powder that is between Cannon Grade, and Fireworks Grade,and designated as Fg, FFg, FFFg, and FFFFg.
Canon grade being the coarsest and Fireworks being the finest.
Also, "Sporting Grade" powder is typically followed by the letter "g"... One very common myth is that the small letter "g" behind the grain size designation indicates that the powder has been graphite coated. The small letter "g" actually stands for glazed powder. Glazing and graphite coating are two entirely different things, but you will find them both used in the manufacturer of Black Powder.
When glazed grains of black powder, lacking a graphite coating, are stored for any length of time the mass of grains will begin to clump together.
The surfaces of the grains are covered in a thin skin of potassium nitrate and charcoal minerals, these are crystalline materials and will behave as all crystalline materials do. When surfaces of the same salt come in contact with even slight mounts of pressure the grains will begin to fuse, or bond, together.
Graphite coatings on the grains act as an “anti-blocking” agent, preventing the grain surfaces from fusing, clumping, or bonding, together.
Sporting Grade powder is "screened" to determine the size, or the number of "F's", as we describe modern Sporting Powder nowadays.
The grain sizing system used in the United States today, was first introduced around 1836 as a means of standardizing grain sizing within the industry.
These sizes were not universally accepted or adhered to until very late in the 19th century. Because of this, we read of the Black Powder used by our forefathers as collectively being of a "Sporting Grade" type.
Under this standard sizing which is the current practice:
Fg........Must pass through 14 mesh... Must be retained on16 mesh
FFg.......Must pass through 16 mesh... Must be retained on24 mesh
FFFg.....Must pass through 24 mesh... Must be retained on46 mesh
FFFFg....Must pass through 46 mesh... Must be retained on 60 mesh
The exception to this is "Swiss" Powder.
Under the Swiss grading of powder, the size will look something like this.
U.S............
Swiss..........
Rough conversion to U.S. Standard Screens.FFFFg..... #1 powder.... 32 mesh to 60 mesh
FFFg....... #2 powder.... 18 mesh to 32 mesh
FFg......... #3 powder.... 12 mesh to 24 mesh
1.5Fg...... #4 powder... 12 mesh to 18 mesh
Fg........... #5 powder... 10 mesh to 14 mesh
It should be pointed out that very small differences in grain sizing does not become significant until one gets into the very fast and very hot burning sporting type powders....FFFg and FFFFg.
As a rule, Firecracker Powder would be upwards of FFFFFFFF or FFFFFFFFFF insofar as any kind of grading or screening system might be concerned. In other words, it is simply to "fine" for anything but fireworks and its "over-use" could result in a explosive effect.
I have heard of guys using it as a fast priming powder, but I don't know this actually happened. I think I would be afraid to use it in any fashion.
Uncle Russ...