Ever heard of a cannononball .. ovoid?

[kronckew]

heated shot was my next guess.

heated shot was as noted used against wooden ships. most fortresses had ovens for heating shot & used well soaked wads to keep the heat away from the powder. firing rates were reduced due to the extra cooling and swabbing required, and as might be imagined, once loaded the cannon had to be fired fairly quickly. accidents did happen. the french built a large number of coastal 'fortresses' consisting of a few guns in earthen embankments, with a small shed for the soldiers and many of these had shot ovens.

i've not heard of it being used in normal land warfare where the shot could roll and be recovered like this one, or i'd possibly considered that. it might have been used in a siege to bombard a town and set it alight, tho i'd expect it to have impact marks.

the health and safety crowd would definitely not allow heated shot nowadays....

Heated Shot

Heated shot furnace