not quite the same topic, but close: the superimposed load was the bane of the sergeants in a massed formation of muzzle loading muskets/rifles during volley fire.
excited soldiers would frequently forget to actually prime their weapon, and not notice they hadn't really fired a projectile, and, to maintain the 'flow' of their rank's motions, would reload a new charge, wad and ball on top of the existing one.
sergeants would, during lulls, have their squad drop their ramrods down the bore to see how much stuck out. one recruit was found (american civil war) to have had six loads in the barrel.
the sergeant would not have been amused. worming out charges is not fun. especially if you are being shot at. even worse, while being berated by an angry noncom.
i haven't decided if the recruit would have preferred to at some point in the making of the stack, to have primed and fired (and blown himself up) rather than suffer the wrath of his 3-striper.
oddly enough, the advent of self contained cartridges did not stop this effect, just reversed it a bit. recruits would forget to actually reload and would merrily recock their actions and dry-fire their way through a battle... again, if caught their sergeants would not be amused.