I don't know why anyone would want to use FFFF for loose powder loading in a C&B or in loading metallic cartridges when FF and FFF are available. Even if not readily available, using FFFF grade isn't a safe practice. You don't put diesel fuel in your gas powered vehicle or vice versa if one isn't available. From reports and written material available doesn't sound like a safe practice. Sure, you might do it and get away with it (for awhile), but you can also drive a vehicle a 100 mph down a gravel road and get away with it (for awhile), but disaster will catch up with you in the end. I did see the end result once of a idiot who did attempt to do 100 mph+ on a gravel road once while a LEO, didn't work out to good for him or his passengers.
The manufacturers of BP specifically say that 4f is for flintlock priming only.
wM1
Shooters take heed. "May not have a harmonious outcome" if ya try to use other than for priming. New shooters to using black don't take this post of using FFFF grade powder for loading as 'the thing to do'! Old time shooters and posters to this forum, IMO, suggesting or promoting using FFFF for loading black powder firearms or in those that may be strong enough to use either black or smokeless isn't a good idea-may give those who aren't aware of consequences, restrictions, etc, the idea to do so is OK. IMO suggesting to do so or the possibility to do so is irresponsible. Of course there may be or will be the tough tobacco chewing, 4-wheel drive, beer guzzling, macho, I can and will do anything types who will do it and decry anyone who says anything against it.
My 2 cents and sticking with it. CC