[DJRowley]

Basically, to calculate damage, imagine a circle with the Secondary Damage radius. Everything within this circle will recieve the Secondary Damage. Now imagine another circle with the primary damage radius. Everything within this circle will recieve the Primary Damage in addition to the Secondary Damage.

You cannot have two different damage types on the same weapon. But you can be cunning (only works on projectile weapons). IIRC, the actual Projectile object (eg. GenericTankShell) can be given a FireWeaponWhenDead module:

  Behavior = FireWeaponWhenDeadBehavior ModuleTag_XX
    DeathWeapon   = SecondaryWeapon
    StartsActive  = Yes                      
  End

Simply make a new weapon which has the other damage type you want and specify it in the DeathWeapon field. As it is just basically an explosion you don't need most of the fields for the weapon entry though, eg.

Weapon SecondaryWeapon
  PrimaryDamage           = x.0
  PrimaryDamageRadius     = x.0
  DamageType              = EXPLOSION
  DeathType               = NORMAL
  FireFX                  = SecondaryWeaponFX
  RadiusDamageAffects     = ENEMIES NEUTRALS NOT_SIMILAR NOT_AIRBORNE
  DelayBetweenShots       = 100000        ; time between shots, msec
  ClipSize                = 1            ; how many shots in a Clip (0 == infinite)
  ClipReloadTime          = 0            ; how long to reload a Clip, msec
  AutoReloadsClip = No 
End