From Re - enactment experience - I did see empty paper cartridges blown out of the musket in perfect shape, no burn and not even a tear.
I always assumed that only a part of the black powder is igniting anyway (about two third.
Again from re - enactment, overloading my Jäger rifle, with black powder only, I could produce a recoil by the left over black powder which did not ignite and I would see the spirals of black powder (left overs) out of the rifle.
As to whether the canister ruptured in the barrel of a gun cannot be said at the moment. so far nobody can prove that it did or did not.
It seems that people get attacked by dogma in case they believe that it did not rupture in the barrel. I find the idea very interesting and thought provoking.