I spent some time documenting the references to Chaos Dwarfs within the Storm of Chaos supplement from 2004.
Check it out:
https://chaos-dwarfs.com/wiki/index.php?title=Storm_of_Chaos
If I am missing any references, please let me know!
I’m working on a YouTube video with the Hellcannon as the focus.
Thanks in advance!
Nice work! White Dwarf #292 had an editorial article on the Hellcannon. In the article the editor references the novel Magestorm by Jonathan Green for how the machines are created… which I was not aware of (still available as an eBook through the Black Library)! Interestingly, the editorial notes that any of the 3 plastic templates can be used when it fires, which is a detail I wasn’t aware of either. Issue #293 has a little on the background, but I don’t think there’s much more that wasn’t covered in the Storm of Chaos book… although I think issue #294 was the first time an ad was shown for the kit. That same issue also has a 6000pt battle report with a Chaos army containing a couple of Hellcannons and a little more about their use in battle. Of course the Hellcannon appears again in issue 295 (including WIP construction of the kit and gap-filling), but after that I don’t think there’s a mention or even a single picture (or ad) of the Hellcannon again until issue #301, with the Storm of Chaos article “The Battle of Middenheim”, where it’s mentioned that the dust is settling on the Storm of Chaos worldwide campaign - a subtle nod from the studio that they’re moving on.
~N
Amazing! Thanks for those extra details, I’ll investigate those. 
The Hellcannon used both templates when shooting - the 3" for flattening everything (intended for castle walls) and 5" for making the defenders run away. The third template would be the flame template for when it would spew ichor if anyone got too close.