The Gadgeteer

[stoutstien]

Arcane Firearm
5th-level Artillerist feature

You know how to turn a wand, staff, or rod into an arcane firearm, a conduit for your destructive spells. When you finish a long rest, you can use woodcarver’s tools to carve special sigils into a wand, staff, or rod and thereby turn it into your arcane firearm. The sigils disappear from the object if you later carve them on a different item. The sigils otherwise last indefinitely.

You can use your arcane firearm as a spellcasting focus for your artificer spells. When you cast an artificer spell through the firearm, roll a d8, and you gain a bonus to one of the spell’s damage rolls equal to the number rolled.

Emphasis mine.

Just what text have I ignored?

Please don't insult. It is a violation of forum rules.

Read it in context of the setting in which the class originates and it fixes it. KB himself has covered this on his blog.