Bullets you can make from stuff too. We need propellant control. But then everyone will switch back to knives and blunt objects. What we need is kinetic energy control.
Newer powders are hard to make, but black powder is actually relatively easy to make from what I understand. You certainly won't be shooting modern quality ammunition, but guns are still possible. The .38 special was originally a black powder cartridge if I'm not mistaken. That's why the case is so large compared to the actual quantity of modern gunpowder that you use.