I was simply using that as shorthand for the type of story under discussion, as well you know! 
Great - thank you!
I seem to remember discussing this with someone. I think the medival paradigm is that size adds damage not speed so a pea will do as much damage if launched form a pea-shooter or a rail-gun.
So a boomtube in paradigm wouldn't theoretically work.
Back on topic,any spell that would help the gun/blunderbust user?
In 4th ed, I ran an alternative saga setting based off of "Sky Galleons of Mars", and I had the concept of the projectile itself (cannonball) being enchanted rather than the weapon. I translated this into a short story I wrote years later; the one side kick carried a pair of automatics, a 9 and 10 mm, and the bbullets had runes engraved on the lead tips by the magus she accompanied. IRL, modern gunfighers sometimes mark an "X" in the lead to allow for a better spread of the projectile upon impact.
So, spells and enchantment on the projectile could be used to increase damage &/or accuracy perhaps.
There is a Flambeau spell guideline in Societas which seems to allow a stone to be projected with more force (+5 damage per magnitude). It doe snot however state (so that i can see) if the stone actually needs to be bigger.