Big Mike
Your quote - "'munitions of war' ... so you are saying no one is allowed to discharge a firearm from a civilian helicopter? "
As stated the law is clear about not using "munitions of war" in civvy aircraft. This basically covers any firearm that is intended to do harm to someone"
The other category that you have is "Sporting weapons" - things like hunting rifles, shotguns etc. I don't think there is anything in ICAO that specifically prohibits use of sporting weapons from a helicopter, however methinks that you would need an exemption / permission from the CAA for such an activity - - maybe deer culling or something like that - i know it goes on all over the world but i'm not sure if anyone does it in UK.