Dusty Coalhopper

As the others posted, the "a" designation is powder that is typically meant for blasting or fireworks. The "g" designation is for sporting or recreational shooting. The "g" stands for glazed as I recall. Recreational powder is polished or 'glazed' to remove the burs and help it to pour easier. (graphite is often added to commercial recreational powder as well) Plus the glazing process changes the size of the grain. All said and done, this process does slow the burn rate down so FFg does not have the same burn rate as FFa. As you might imagine those who dabble with making their own are likely working with more the 'a' variety as most wouldn't bother with the trouble of polishing powder. But most are screening the powder to be equivalent to the "g" size categories.