Also, with good materials technology (which seems to exist in this setting) compressed air and possibly even exceedingly powerful springs can both provide options to gunpowder. There were compressed air repeating rifle during (IIRC) the Napoleonic Wars.

I rather like the idea of having guns that don't use gunpowder. Using compressed air would also make field artillery impossible and automatic weapons considerably more difficult and less deadly, both of which are features that fit the setting quite well. Then again, I've always been a fan of Andre Norton's Witchworld with dart guns, swords, and chainmail.