Another option is, by the way, technomancy. Gunpowder isn't the only possibility for the propelling force of a projectile from a barrel; fire mages wouldn't have trouble using something like micro-explosions that they generate themselves. It's even quite possible that this path will be much more obvious for them and quite competitive with combat magic. Because throwing a fireball far should be relatively difficult for a mage; not everyone can do it, but exploding something in their hands so that it propels a projectile forward – even a weaker mage can handle that.
In the world I worked on a long time ago for a forum, specifically for dwarves, I actually used both of these ideas to make them technologically advanced.