I am building a world in which technology has taken an enormous step back due to an apocalyptic event. For one reason or another guns no longer exist in the world and I would like to have a reason why they could not be created/used again, even given enough time for technology's advancement once again.
I would like to leave the atmosphere alone but maybe remove a resource that would in-turn make the production of guns impossible. I wouldn't mind if ammo was the cause of guns not being used instead.
I don't know much about firearms so I'm not sure if what I have explained makes much sense but any help is greatly appreciated! Cheers