In worlds with the "Drunk World" seed, in which both Silver and Tungsten are present, the arms dealer will sell the bullet corresponding to whichever ore is most prevalent in the world upon joining. This reset every time the world is re-opened.
Tungsten Bullets were added so that a world with Tungsten Ore can make a Silver Bullet (Tungsten's counterpart ore) equivalent without utilizing an Extractinator or crates.
Tungsten Bullets have a knockback rating of 4, while Silver Bullets only have a Knockback rating of 3. This is reflected by the fact that Silver Bullets are 16.66% cheaper to purchase.
Despite the fact that Silver Bullets are cheaper than Tungsten Bullets, both ammo types sell for the same amount. This has made the Tungsten Bullets sell for 1/6 of their buy price, which is inconsistent with other sell prices.