I can see how the convenience of a vending machine might be appealing, but I'm really not in support of this idea. When it comes to something as serious as ammunition, I think there needs to be more oversight and a more responsible process than just a machine dispensing it.
Vending machines work fine for snacks or drinks, but there's a lot more responsibility and regulation that should go into purchasing something like ammo. It just feels too impersonal, and I'd prefer there be more direct interaction and accountability in situations like this.