Round lamp or ??

Near a civil war battle/camp site today. Found a ball type thing. Very fragile like thin brass or copper maybe. It is hollow and fell apart in digging it up. Has a core type thing like an oil lamp but is not much larger than a golf ball. Thought maybe a bell because had a rusty thing inside of it. No holes for sound though. Part of it is missing but tried to piece it back together to see what it could be. Bullet is in pic for size reference. Anyone seen a small round oil lamp like this? Seems too small and too round to be very useful. Any ideas??