[quote=@Abillioncats]
<Snipped quote by Lugubrious>

It could make a crater roughly the size of an average sized house. 
[/quote]

If that's the case, then I would say that an upgrade for a cannon that uses 25% of your character's aura would be a major armory upgrade.  Losing her whole aura would be a small price to pay for ending practically any fight instantly, if she shot four times in quick succession at a single target.