WOW!! that's amazing that the larger charge of Pyrodex P with a lighter projectile would be slower then Pyrodex RS and a larger projectile. Very interesting testing results to say the least. It almost makes me want to get a chronograph for myself, but that might cause me to shoot more..
I wonder what did that? I always thought that cool weather would help with velocities (though i don't know from experience), and then, like you said, more powder of finer granulation and a lighter bullet. Maybe there was blowby with the 385s? But they were so much harder to load. Maybe they had more resistance with the bore? The lube on the buffalo brand bullets is sure enough slick. I'd give a shiny penny to find out.
Happy Hunting, Phil