This is ammunition for your Revolver. Boxes of revolver ammo occur almost as frequently as flintlock gunpowder and bullets. However, each box only increases your revolver ammo by 5 bullets, so it will take a total of 41 boxes to fill your revolver ammo up to the maximum amount. This means that, early on, you should try to conserve your ammo and wait until you've got a decent amount before using it a lot.
We're Getting Mutants in the MCU - The Loop
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