Being that the supposed military etymology of the brass monkey story is universally cited as coming from the navy, my logic is sound.
Personally, I'm predisposed to believe it's BS for the temperature/physics you cited, but you can say only that it's pretty unlikely for Naval
storage of ready shot. History has one, perhaps two
, examples of cannons being used from fixed fortifications on land, and it's perfectly logical
to have a ring of some sort to hold four balls, either beside the gun or by a furnace if one were to heat them before firing.
I'm just not as predisposed to dismiss something as illogical simply because you choose only what fits inside the story you want to tell.
Either way, feel free to jump in with the last word if you're really pumped about the topic.