Naval swivel cannon, Indonesia, 17th or 18th century AD

Funnel to make loading easier, maybe? Swivel guns were typically fired relatively quickly, so speed of loading/reduced precision needed could have been an advantage. Swivel guns, as relatively close-range weapons, could also be stuffed with grapeshot (or just debris in a pinch) for a shotgun-like effect. Easier to pour down a bunch of little bits and pieces down a funnel than a narrower opening.