When you finish a Long Rest, you can use Woodcarver's Tools to carve special sigils into a Rod, Staff, Wand, or Martial Ranged weapon 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 1d8, and you gain a bonus to one of the spell's damage rolls equal to the number rolled.