The problem isn't the carrying capacity, the problem is the NPCs watching you put gunpowder in front of them and thinking that's normal, or they arrive at a place full of gunpowder and do nothing.
They've all horribly failed their wisdom/perception checks.
"A bunch of adventurers bringing gunpowder to me, must be gunpowder deliverers. By coincidence, they stopped to rest here on MY SIDE."
