It is true that the Lyman Black Powder handbook shows loads for the 54 cal using 3F. Larger than .54 they used 2F. The experienced people I am referring to, are people I used to shoot competition with at the state competition. Some of these people shot in the national meets at Friendship and also on the international team. The manufactures recommendations I have looked at (I haven't seen them all) recommend 2F in the larger calibers.
My Black Powder Handbook by Sam Fadala says" In one pressure/velocity test, 140 grains FFg rendered a muzzle velocity of 1,779 feet per second with an LUP (pressure measurement) of 8,300. Only 100 grain of FFFG produced a velocity of 1,740-just 39 feet per second less but, a LUP of 11,700.
We all know people that exceed reload manuals and get away with it. I have talked to people who have seen muzzle loaders blow up.
Be carefull.