[Niko_boy]

Since 0.3z you can detect weapon firing state using OnPlayerWeaponShot. So using this you can check like if ammo is like near to or less than 2 ( if(ammo < 2) { ammo about to over } ). Because i am guessing that this callback count every single shot fired.
So maybe this might come usefull.
Else you can use a very quick timer or OnPlayerUpdate which aint the best thing to do though.