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Excellent account very clear.I think you have the process reversed in your mind.
The granulation process is such that the smaller grains and dust falls out first. The larger grains are what is left as the powder is passed over mesh of smaller size - the FF sized grains you reference pass over the smaller mesh size holes that the smaller particles pass through.
The dust / extremely small particles can be collected, moistened (liquored) and re-pressed into mill cake and re-processed through the granulation mill along with the very large 'chucks' that would not pass through the size of mesh screen being used to obtain the desired grain size.
Some of the 'dust' would be used for filling explosive shells or for making fuses.
After the powder has been granulated to the desired size it is in a rough and fractured state as yet unsuitable for use, and referred to as 'Foul Grain' and is coated in dust that would increase the powder's absorption of moisture and contribute to degradation of the powder if not processed further. Foul grain also will not pour smoothly as the rough edges catch and hang up with the other grains. The foul grain moves on to a first 'dusting' process and then to the glazing process where the powder is tumbled / polished to get rid of the coarse or jagged edges so that the powder flows more easily when measured. After glazing, the powder is subjected to a second dusting process. Then a drying process occurs and then a third, or 'finishing', dusting before it is ready to be used as small arms gunpowder.
Regarding another 'myth' - The lower case 'g' refers to powder which has been glazed (polished) and does not indicate powder which has been mixed with graphite. Swiss powder is heavily graphited, which is why the grains are so shiny and silvery in appearance. Graphite is an impurity in gunpowder, and raises the ignition temperature / slows ignition, which in some applications is desirable. Graphite was also used in years past to improve the appearance of inferior quality gunpowder
Regards Rudyard