Perhaps fire arrows like those in the link below were used in the Swedish Loshult cannon, 1340-1360?

I found this forum thread, showing a lot of cool stuff; above all the fire arrows and arrows used in pot-de-fer-cannons, such as described/linked to in these posts:

Die Geschützdarstellungen des Walter de Milemète von 1326/7
Fitting round pegs into square holes?
Cool page about the earliest cannons