Can a multiclassed artificer/rogue use Sneak Attack with spells that use a ranged weapon as a spellcasting focus?

Question

So, according to a tweet by Jeremy Crawford, it is possible to Sneak Attack with a magic stone when using a sling, even though it is a ranged spell attack.

That got me thinking: if an artificer imbues an infusion into a ranged weapon (let's say the Repeating Shot infusion on a hand crossbow, though any infusion on any ranged weapon should work), they can use that weapon as a spellcasting focus when casting artificer spells.

If they use such a spellcasting focus to cast an artificer spell that makes an attack (for instance, fire bolt), would that count as "making an attack using a ranged weapon" for the purposes of features like a rogue's Sneak Attack?

Answer 1

A spell can involve attacks, but the casting of a spell is not itself an attack. Therefore, Sneak Attack doesn't activate

Sneak Attack states (emphasis mine):

[...] Once per turn, you can deal an extra 1d6 damage to one creature you hit with an attack if you have advantage on the attack roll. The attack must use a finesse or a ranged weapon. [...]

If you use a ranged weapon as a spellcasting focus to cast something like fire bolt, the attack isn't using that weapon, the spell is. Because the attack itself is not using a ranged or finesse weapon, you cannot benefit from Sneak Attack.

Answer 2

No, they can't.

Let's have a look at some definitions and rules, starting with the spellcasting focus. Under the Material Components section one can read (emphasis mine):

Casting some spells requires particular objects, specified in parentheses in the component entry. A character can use a component pouch or a spellcasting focus (found in chapter 5, “Equipment”) in place of the components specified for a spell.

Hence, a spellcasting focus is just something used as an alternative to mundane material component: its role is only to substitute such type of components.

The description of Sneak Attack says (emphasis mine):

[...] Once per turn, you can deal an extra 1d6 damage to one creature you hit with an attack if you have advantage on the attack roll. The attack must use a finesse or a ranged weapon.

A first reading suggests that you must attack with a finesse melee weapon or with a ranged weapon: this is confirmed also by the Sage Advice Compendium (emphasis mine):

Can a rogue/monk use Sneak Attack with unarmed strikes? The Sneak Attack feature works with a weapon that has the finesse or ranged property.

When you are casting spells like Fire Bolt using a hand crossbow as spellcasting focus, you are not shooting with such weapon but you are instead attacking with a spell without using that weapon\$^\dagger\$: hence the conditions for the Sneak Attack are not met.

---

There is a spell that allows what you describe.

You may use an hand crossbow as spellcasting focus, cast Flame Arrow on some bolts and then use the crossbow to attack the enemies with the enchanted bolts: the weapon requirements for Sneak Attack are met. Actually, this works whatever your spellcasting focus is.

---

\$^\dagger\$ Pay attention that there are some spells that uses a weapon, such as Booming Blade or Green Flame Blade and may trigger the Sneak Attack, see here.