Don't even think of using smokeless in a flintlock, I don't care how strong the barrel allegedly is. Smokeless must be ignited by a powerful primer, you don't want to simply set the stuff on fire with a spark through a touchhole.
The primer does more than set the charge on fire, it also creates the initial chamber pressure needed for efficient smokeless powder burning. If that pressure is not achieved, you get a "blooper". Sort of like setting dynamite on fire with a match instead of detonating it with a blasting cap, it just burns instead of exploding. If you compensate for the blooper by putting in extra charge so it will burn up to working pressure, the difference between a blooper and a barrel bursting overcharge can be razor thin.
I repeat, smokeless must be ignited by a powerful sealed primer, like in a cartridge, it's not about the weakness/strength of the gun, it's about the ignition method.