Selling Inventory

You can Sell ammo that's in Inventory. Just find the Crate you want to sell ammo from, go to the Inventory tab and click the 3-dot menu next to the caliber you want to get credit for:

Please Note: If you're on mobile you may need to swipe your screen to the left TWO times, once to see the 3-dot menu and again to see the options. Or you can turn your phone landscape to see more. 

Select Sell: 

Just click the yellow button marked "Sell Ammo" at the bottom of the confirmation page to complete the transaction.