子弹 (zǐdàn) vs. 弹药 (dànyào): This is a key distinction.
子弹 (zǐdàn) specifically means “bullet” or “cartridge.”
弹药 (dànyào) is the much broader term for “ammunition” or “ordnance” in general, which includes bullets, missiles, grenades, artillery shells, etc. Using 子弹 when you mean “missiles” would be incorrect.