No No you don't use secondary for a dual cannon here is how you do it:
If you got a dual cannon tank you got recoil bones and flash bones for example lets say it is named Barrel01 and Barrel02 if you want the weapon to fire from both like the mammoth tank you would do the following:
Code:
WeaponFireFXBone = PRIMARY Barrel
WeaponMuzzleFlash = PRIMARY Barrel
WeaponLaunchBone = PRIMARY Barrel
See how their is no number that tells the game to use all bones named Barrel. That way it will use the two barrels to fire from hell you could make 4 barrels.
