The command you are looking for is
fire as in...
myAPZ fire ["muzzle","magazine"]
This is what you need to do. Give your APC a name. Find out what it's guns are called. This information can be found in the
OFPEC Comref. There you will get the name for the muzzle and the magazine.
Most smoke launcers are named
smokelauncher and their magazines are usually called
smokelaunchermag. In that case the above syntax would read something like this:
myAPZ fire ["smokelauncher","smokelaunchermag"]
Note: The exact syntax may be a bit different. I wrote this from memory. But it should give you something to start with. Good luck.