There was a thread in this forum that showed that there was a contradiction when the velocity of 777 ffg was compared to the velocity of 777 fffg in a rifle.
It was a surprise that the 777 ffg produced the higher velocity when chronographed.
That may be because 777 doesn't like to be compacted, and the ffg is harder to compact.
That's what makes muzzle loading really interesting. There's exceptions to rules, and the performance of 777 fffg contradicted the rule that applies to all of the other powders. At least in that case it did.