@Jackgiantkiller I don't allow firearms and never have. Players feel like they should just kill anything in one shot, and I really don't like them in a FANTASY setting. I use the different laws of physics so gunpowder doesn't work reasons. Magic rules over technology such as this.
As for other arms and armor advancements, there are other things out in the world that would encourage the development of plate armor and later weapons (rapier, etc.).