Empty Bullet

Loading a gun with these does nothing. They are only a base. Every specialty Hardmode round is built on top of them, so the moment you start making your own ammo you buy a stack and stop thinking about it.

The awkward part is the other half of each recipe. The additive comes from a different vendor for every round, so covering the full range means keeping several NPCs alive and housed, not just the Arms Dealer. Work out which rounds you actually want before you build the town around it.

No NPC sells anything cheaper on current versions. The name is also wrong: what you are handing over copper for is a complete cartridge, not a bullet.