Dwarven WarHost::
At 500pts the ballista is going to be more of Bringer of 2 rounds of Joy or Sorrow. I've always suggested that one add a 3rd model to a Dwarven Ballista (68pts), helps to move it about at the full 5" movement rate.
You'll need to have it pay off that quickly because after that you're going to find your targets are going to be within the 3" scatter range, with most of the new scenario's setups, making your 60pt weapon sink...useless. You could attempt to move the ballista to a better vantage point, but again, in the time it takes to move it your opponent will have dedicated a small task force to eliminate the crew or just move his forces within 3" of your forces and basically ignore the weapon. ((good forces can't fire siege weapons at the enemy if other good models are within the weapons, potential, scatter range))
A ballista is nice, but in the right situations (ie. larger point games).
Suggestions: Drop the ballista and Hornblower. Pickup some more troopers and +/- Banner Bearer.
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