Necklace of Fireballs

This necklace has 5 beads hanging from it.
You can use an action to detach a bead and
throw it up to 60 feet away. When it
reaches the end of its trajectory, the bead
detonates as a 3rd-level fireball spell
(save DC 15). You can hurl multiple beads,
or even the whole necklace, as one action.
When you do so, increase the level of the
fireball by 1 for each bead beyond the first.