Silly Putty
Superglue
Kevlar
All items designed for a purpose that were found to be useful in an originally unintended way.
Money made of precious materials gain their worth from the materials they are made of, not the other way around. If I showed up at a shop here in the town I live in with a gold coin and a lump of gold, I could use either to exchange for another item because gold is widely regarded as a valuable material. Items can be used for purposes both intended and unintended. If bullets were widely regarded as valuable then why would it be so unbelievable that someone could use them as a means of procuring goods and services (aside from robbing people that is).
Yeah... but none of them are
money.
Which of these would consider a crate of bullets more valuable?
Julie Farkas, or Pacer?
Pacer, obviously. He's part of the Kings, and bullets are useful for putting down chemmed out thugs and pushing around undesirables. Far less useful to Julie, who is a healer first and foremost.
Now.... Which of them would find a bag full of bottlecaps more valuable?
Both would find equal value, because it is a
liquid means of exchange, not a consumable good. Julie can use them to procure more medical supplies, and Pacer can use them to procure more bullets.
Now, Julie could barter those bullets. But to whom? Anyone? Nope, only those who would in turn have a use for them. That's the definition of bartering: exchange of goods or services without a monetary medium. She may get lucky and find someone with a cache of usable medical supplies, or she may just simply trade for....
bottlecaps.
The express purpose of money is a liquid means of exchange. The express purpose of a bullet is to be shot.