I think using the
someAmmo command will prove more trouble than it's worth, because it only becomes
not true when the vehicle is out of all possible magazines. In other words, your chopper may use up its rockets but, as long as it can fire its gun, it won't rearm.
Use the majority of Raptosaurus' script, but, as you originally wanted, have it looping every three minutes:
_craft = _this select 0
_mags = magazines _craft
#start
? ! alive _craft : exit
{_craft removeMagazine _x} forEach _mags
{_craft addMagazine _x} forEach _mags
~180
goto "start"