i feel it's a hand cannon myself, the rough bore would not be unusual after all these years of relative neglect and corrosion, probably was a bit more regular when 1st made & used.
they'd use pretty crude powder, grass wadding and convenient sized rocks for ammo, iron and lead shot is a much later application for sophisticated matchlock and later wheel locks when bores could be controlled better during mfg to reduce windage...
additionally, it was expected that the odd hand cannon or two would blow up (variance in powder quality, payload, corrosion due to poor cleaning, poor craftsmanship techniques, double loading*, etc. one reason fro a LONG stick. the bands not only held it to the stick, but kept some of the chunks of a burst barrel from zapping the shooter or those alongside.
the short barrel while not allowing maximum velocity, would give less chance of a shot sticking or jamming and blowing up the device, while still producing a satisfactory BOOM, smoke and such to frighten the horses, and if really lucky actually have the projectile hit and damage an armoured man.
of course my muzzle loading experience started with cap and ball rifled muskets & pistols, a much more modern approach.
*- one rather embarrassed yankee pvt. in the civil war was noted to have loaded his musket about a dozen times without actually firing it, each load rammed down on the previous one. luckily he DIDN'T remember to cap it before he pulled the trigger or it might have been less humorous... of course the confederates would never do such a thing
, wastes ammo.