1) place an object on the ground, or below the ground and use this in a trigger:
chopper dotarget object; chopper dofire object
where chopper is the name of your bird, and object is whatever he's shootin at ....
(this may or may not work with the chopper)
2)Uhh..... add custom music.... there are tutes.... and a whole board of the forums dedicated to sound and cutscenes
3) camcreate the shells
trigger:
bomb1="Heat120" camcreate getpos obj
where obj is the spot where you want the shell to appear....
( you can use any object , or a game logic point )