Wasn't the Iowa incident during a rapid fire exercise, and the blame placed on not using (forgetting the step of) compressed air to clear breech/tube of embers of the last powder bag?
Placing new bag(s) atop glowing fragments might enable a "cook-off" of the powder before the breech is closed, and with a shell blocking the tube the guys in the turret are literally cooked?
One can't discard a disgruntled (new buzz word) sailor who may have exacerbated circumstances which may have led to an "accident"?
In more than just these cases....tanks, mortars, handguns, (incidents in other turrets/artillery pieces/ammunition storage)...
A DFO as an explanation is SOP, but there remains other possibilities.

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