Why Gaston didn’t use his gun
Disney creators are known for their meticulous attention to detail, and they make every effort to stick to facts as much as possible. That may seem strange, given how many Disney films occur in made-up worlds populated by talking animals and magical creatures. However, it helps in the credibility of the storylines.
Consider the following scene. Why would Gaston use a bow in this battle if he is known as the best shot and is constantly armed? To be honest, it was raining. Gunpowder and water do not mix.