I have seen old drawings of Men of War gun decks with shot heaped in piles. I suspect that this may be styalised or dressed for harbour inspections though. "IF it moves - Salute it. If it doen't - Paint it !
I concur with the thoughts that the real differential of expansion makes no odds, and that with the normal motion of a sailing ship in a seaway only the most naive of people would expect shot to stay in neat pyramids.

On personal experience a pile of beer cans will move in a yacht - best kept lying on their sides in the bilge to keep cool.

Gareth