in battle screen you have additional numbers per ammo slot (visible only when used).
for inventory is it bit lacking, I did not made yet how best to display it, one solution is add loop in ammo popup that will show all loaded ammo in sequence (1s -> first slot showed, 3s -> second slot showed, 5s -> third, etc.)
another is add postfix to display name of weapon based on loaded ammo, something like that: "pistol (with explosive)".
other solution could be adding ammo count to each weapon in inventory (not in stack on ground) similar to battle scape.