With FPS's its a good idea to reload your weapon when ever you get the chance. But the way you have trem set up is that it waste what ever ammo you have still in the clip. This is really bad for the shotgun. Say you just killed a goon and you have 3 rounds left. You need to reload or you won't kill anything before you automatically reload. However when you hit R to reload the 3 shotgun rounds dissapear.
I suggest that you change it so that instead of discarding the rounds it merely gives you a partially full clip. This will be good if you have to make a run back to base but are low on ammo.
Sounds pretty okay for the shotty, it's realistic and such to add more ammo.. But in real clip based weapons like rifle, how do you add some extra ammo to a clip? That would be time consuming and require that you carry extra ammo that's not in clips... I had this same idea but then I realised that it's actually unrealistic.
Only thing that I actually think would be good addition is: No reloading possiblity if clip is full, this would prevent accidental ammo wasting.