The Fg rating is a more modern system to define the grain size of BP .The difference between Cannon , Fg ,Ffg , FFFG, FFFFg all the way up to 10Fg is the grind. it�s the same powder just a finer grind . The smaller the grind , the more complete the burn of the powder grain . Thus the higher the pressure , which in turn increases velocity to a point .
The FG scale came about really more as a way to define and regulate charges for BP cartridge , then it was for anything else . It provided a more consistent way to define an average size of grain .Prior to the scale , you had musket grade and cannon grade/ corn grade powder with larger and smaller grains spread throughout of 1F / musket powder as well as also small grains .
BP is measured in volume based on the reasoning that it is produced in Cake which is a given volume . Its is then ground and sifted through screens to produce average size , NOT pressed to a given size or flake as with modern powders .
There is no more , nor no less powder by volume then what the original grind started with . Again , by grinding that original cake smaller , a larger surface area is produced . Thus increasing the chance of ignition and creating a more complete burn . IE, why you get higher pressure from 3F vs. 2F even though it�s the same powder .
Yes you actually use alittle less . Also what you see coming from the muzzle , isn�t always un burnt powder . For the most part its un burned carbon cinders
Myself
I use 3F in everything from small rifles to large bore 60-79 cal � IF � that�s what produces the best accuracy .
Myself I prefer 3F when I can . Not only does it take less but I also find it cleaner .
The reduction of 10% between 2and3F isn�t exact. It really depends on the powder . All the barrel cares is that it has X pressure . As such if you fine tune your 3F load so that it produces the same pressure as your 2 F load , its will shoot very near the same . Might not be exactly the same do to the slightly quicker pressure spike . But again that happens so quick most folks wouldn�t even know
With that being said, Myself I prefer 3F . However I do have a couple rifles which prefer 2F . I just never have been able to produce a 3F load in those rifles which will produce the same target accuracy of the 2F . Close , just not good enough .
The theory that your being told by Dixons is one of 2F gaining more surface area to initial ignition .,
Cant say I agree . Now in wet conditions , 2 F doesn�t get wet as fast as 3 F or 4F . But when dry I don�t find it lights any easier then 3F .
Some folks also say that 3F is just as fast as 4 F in the pan .. Half of one , dozen of another . I use 4F in the pan and 3F when I find myself without 4F
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