Mortors precede cannon, and remain more effective until cannon become a
useful battlefield weapon. Mortors are typiclly loaded with flamable debris
or with rocks rather than a single shot.

Weapons on deck tend to make ships top heavy. Reduce the sea-worthiness

All weapons are smooth-bore until the 19th century level of technology.
Rifeling exists during the earliest gun powder era, but requires alot of
skill and time to use effectivly. Bird hunting and marksmanship contests
were the only applications of rifling for a long time. Riflled muskets come
in the 17th century for hunting medium game.

Notable improvements came once every hundred years in hand held firearms,
perhaps once every 50 years in cannon.

Kenneth Gauck