I wouldn't make it one shot. I also disagree with you even thinking of the chariot rule of autoexploding. I would give it impact hits. Either d3 or d6, but not too many attacks (4?).
A cannon could work, though what you've drawn seems more like a camera
![icon_wink :icon_wink:](http://warhammer-empire.com/theforum/Smileys/phpBB/icon_wink.gif)
Having a pilot at the top reminds me so much of Labyrinth. I loved that clockwork giant with the crazy goblin in it.
Am I the only one looking at your gobbo/dwarf threads?
![engel :engel:](http://warhammer-empire.com/theforum/Smileys/phpBB/engel.gif)