Help wording on a pepper box gun

[stoutstien]

So I had an idea for a item used by an artificer that is really just a pepper box gun loaded with blowgun needles. was thinking of trying a new way of working with saving throws. So it would be the standard 15 foot cone with the save DC 8+Prof+ int/Dex and I want the damage to increase with the lower the target rolls. So every number lower than the save DC =1 more needle hitting the target+ I don't know 3 damage on a save. (If they are unable to roll a ST it results in max damage.
Note this would be a once a short rest concept due to loading would take at least 10 min.
Thoughts?
Just realized posted on wrong forum.

[Spectrulus]

Having a gun slinger replicate the effect of burning hands but with needles is fine, make sure to make the cartridge at least as expensive as requesting a 1st level spell, probably like 10 gold a cartridge in parts. 3d6 piercing, save for half, probably 1-2 hours to craft.

Having the damage scale based on how low the save is, while okay, is a lot of math and could slow down a table, I wouldn't go that far.

[stoutstien]

I think I'm going to use the extra die of damage for every 5 Points below. Good idea being fueled by spell slots.