I had thought about it the other day, and a few friends liked the idea.
I know the whole idea with the Spiral Knights and their guns are that they are small side arms and that is why something like the Magnus knocks them on their ass, but if the gun made you stand still and gave you a decent amount of knockback (as in, you slide a bit), wouldn't that make the logic part of it make sense?
Now I know the Autogun series kinda already has bullet-spraying, but it sprays like... Well, a machine gun/machine pistol. But this thing would maybe have a more settled spray. Not to mention, the pellets would launch all at once. Maybe to make it less viable to catch dodgy things in the spray (being that they fire all at once) give it a slightly tighter cone of spread?
I'd imagine this gun would do normal or piercing, but maybe a chance to stun would work, too.

Anyway, throw out opinions and ideas. Chances are whatever comes up in this thread, no matter good it may be, will never see the light of day in the game anyway.