Silver Bullet

Before hardmode the Arms Dealer only stocks these while a blood moon is up, which is exactly the night you want them and also the night you least want to be standing around in town. Buy deep when the window opens. Once the Wall of Flesh is down they sit in his list permanently and the timing stops mattering.

This is the one reason to think twice. Weapons that rewrite basic bullets into something better, the Uzi and its high velocity rounds being the obvious case, do not recognize these at all. The game treats them as a separate projectile entirely. The tungsten version you get in the other world type does convert. So if your gun transforms its ammo, load musket balls and save these for weapons that just fire what you give them.

They light their own path, which matters more than it sounds when you are shooting into an unlit cave and want to see where your shots are landing. And they tear through werewolves, so a stack sitting in the ammo slots turns the worst part of a full moon into a non-event.

If you are buying musket balls and converting them at a bench, stop. Buying the finished ammo outright costs less. The recipe exists for players sitting on raw ore, not for players standing next to a shop.