I found these pics of a nicely scratch built Hellcannon from an old WoC blog, I apologize if they have been posted before. Here the links of the blogs:
Restless Wargamer: Scratch built Hell Cannon pt2
Restless Wargamer: A few updates
I don’t remember ever seeing it before. Looks to be a very effective rendition
Looks more like a scratch built Earthshaker to me.
Not a bad job at all. The angles and cuts are very precise and well put together.
Nice. Has a bit of both hellcannon and skullcrusher to me. Well done on both accounts.