all you have to do to reload a tank or some other such vehicle.. is use these commands :
(This example is for the AH1)
_unit removemagazines "HellfireLauncherCobra"
_unit removemagazines "ZuniLauncher38"
_unit removemagazines "MachineGun30"
_unit addmagazine "HellfireLauncherCobra"
_unit addmagazine "ZuniLauncher38"
_unit addmagazine "MachineGun30"
substitute the _unit for the name of your vehicle that is being reloaded..... and the bit in quotes should be the weapons used by the vehicle you're trying to reload