as much as 99% of the powder would be consumed just past the peak of the pressure curve
That sounds right for rifles.
I spent a couple of fun hours just fiddling with the NABM software, just to see what is possible. IIRC, you could get combustion the full length of a rifle barrel with a really big load of really slow powder. I couldn't find any practical loads that would do that.
Of course, if they did, there is the question of whether they would kill more moose in Alaska....
So if we adopted Keith's suggestion of running a tube up though the center of the cartridge to ignite the powder from the front and then use back pressure to hold all the powder in place
All of what Rocky said, plus it wouldn't work because the whole case is pressurized, with the propellant gas filling the space between the granules.
OTOH, I've wondered about dissolving powder in solvent, and depositing a shallow disk of solid propellant in the rear of the case that would burn longer than the granules, in effect creating a sort of duplex load that would have a component that burned longer. Just silly daydreaming, I suppose.
