You can heal during combat by using stim shots.
The browser only knows that you click "shoot", it has no idea if it actually works (it doesn't if you're out of ammunition, or the weapon jams, or various other possibilities). Keeping the inventory open does not cause an extra database hit, since it already has that particular slot to handle firing. It updates the single affected slot already. There are two major complications:
1. You can have multiple slots with ammo.
2. You can multiple slots of multiple TYPES of ammo (in this case, it's actually different items).
That said, I've been thinking about how this might be safely implemented anyway. I won't be making any changes for it today. 
For bounty hunting, the fights will be simulated when you are "attacked", but when you attack somebody to collect the bounty it will be a normal combat for you. As the victim, you will fight with whatever you happen to have equipped at the moment you are attacked. Being attacked for bounty won't affect your ammo, either. Having the server "take over" the combat is a tricky thing, and it's also something very few people would probably want to happen.
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