This is Mons Meg, a six-tonne siege gun that was state of the art in…1457.

When was gunpowder invented? Is it true that the original invention was by the Chinese for fireworks and they never thought to use it as a weapon?

D&D allows gunslingers, but not all GMs do. If you’re writing a fantasy novel in your own world you can, of course, do what you want with guns.