The development of firearms did not take place until after the initial Gith invasion. Both the orcs and the gnomes had experimented with them, but the orcs found them to be boring and cowardly, while the gnome artificers were more interested in making self baking ovens. Due to this lack of interest, gnomish forces had to jump start all languishing projects when the Gith invaded, and were pushed to accept help from dwarvish and elven artificers, clerics and arcane specialists for time management.
Unfortunately, gnomish forces had initially focused on using magical ammunition with elemental effects that had disastrous results. Even with corrections made to elemental components removed from firing mechanisms (unlimited ammo) and to the ammunition (fire & ice damage), it would take almost three years before testing on the battlefield would begin. By the time rifles and cannons were introduced on the battlefield only two years remained in the conflict - at least on a world-wide scale.

After the Gith had vacated Grage, it was agreed by allied forces that though this technology was initially ineffective, these weapons were easy to produce and train with... and the fact that a mere commoner could kill a skilled wizard, or even a hardened barbarian with one good shot was destabilizing to society enought to halt further study and distribution of all firearm forms, ammunition and smoke powder. The four shot revolver that is mainly carried by Artificers is considered a magical weapon by the common humanoid.

Now that I am a fossil, it was weird seeing 5E D&D gain mainstream attention and it peaked my interest. Eventually I ended up in an OOTA group of 20/30 somethings from 2nd level all the way to 16th for almost 5 years. Throughout this campaign we dealt with faerzress and wild magic brought me back to wanting to create a campaign world that is not damaged, but still functioning and still under threat of destruction from the same enemy. As much as I wasn't a fan of Independence Day: Resurgence, I think of Grage similar to that movie with a slightly less lethal but much more powerful enemy and a still divided world that is now post-united against a common enemy.