This is how to make when you activate a pack, it mounts a weapon with ammo.
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BadShot-

 Create the weapon Image and ammo datablocks, then specify the weapon Image in the pack 
datablock: 

weapon = "NameOfWeaponImage"; 

now in the onActivate function for the pack, add these lines: 

%obj.setInventory(%data.weapon.ammo, 50); 
%obj.mountImage(%data.weapon, $weaponSlot);