Can a world run out of bullets?
I've been wondering about how a modern/futuristic world can revert to melee weapons. Other fictional worlds have come up with their own solutions (personal shield in Dune, the Force for Jedi in Star Wars, everyone being hopped up on bulletproof steroids in 40k), but one avenue I've wanted to explore is: Can a world run out of bullets?
Suppose a world where direct energy small arms just aren't feasible. Maybe the energy efficiency is too low to justify the cost of making a laser gun, or people just never figured out how to miniaturise a plasma generator. There are plenty of good reasons to deprive a world of direct energy weapons. So the world uses gunpowder firearms, like today.
Bullets require a propellant and a projectile. Usually the projectile is made out of metal. If you want a world to stop using bullets, you could say that it ran out of metal. But then you'd harm a lot of other industries important for the world to remain modern or futuristic. So "no more metal for bullets" is out.
What if the world ran out of propellant, then? From what I understand, propellants are made out of chemicals such as nitrates and sulphates. Perhaps you could say that people mined too much and now the world is stripped of such chemicals to use as propellants. Yet, many of these chemicals can also be synthesized.
How would a world run out of bullets?