IIRC 3e had cantrips for flinging any small object or specifically arrows and crossbow bolts as well, which would logically be adaptable as slightly higher level spells to fling a cannonball or shell directly or as a triggered item effect, rather than muckin' about trying to use fire spells as the charge in a cannon. One of the ideas I had but never got around to before burning out on class-and-levels fantasy entirely was to turn a quiver into a Wonderous Item that was basically a wand for the arrows version combined with the ability to hold the actual ammunition. Undoubtedly the kind of impractical thing that by the time you can make it as a character it's all but useless and no DM will allow having commissioned at lower levels, but eh. Insert that comic about wizards leaving shotguns lying around all over here
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‎noli esse culus
‎noli esse culus