Found a bug while using The Wrangler, unsure if it affects other guns. Whenever I bought ammo for The Wrangler the amount would update in my inventory, but when entering battle the number listed in the "Attack With Your Weapon" line would not update. This caused the game to tell me that I didn't have any ammo despite me having some in my inventory. At one point it even told me I had -3 .22 rounds in my inventory.
I found an easy fix for it once it happens, just reequipping the weapon seems to force the game to recheck how much ammo you have for it and will update properly. I had to do this every time I bought new ammo.