any bow or firearm of fireball, +0, +1, +2, or +3

This bow has a number of charges based on rarity (table below)

On a ranged attack, you can use
an action to expend 1 of its charges to cast the
fireball spell (save DC 15) from it. For 1 charge, you
cast the 3rd-level version of the spell.
The bow regains (table below) expended charges daily a·
dawn. If you expend the wand's last charge, roll a d20.
On a 1, the wand crumbles into ashes and is destroyed.

at higher rarity the number of charges increase by 2 for each rarity above common.

at rare you can increase
the spell slot level by one for each additional charge
you expend.

 

rarity	Extra fire damage	charges	Charges regained
Rare	2d6	7	1d6+1
Very Rare	3d6	9	1d8+1
Legendary	4d6	11	1d10+1

 

		15	1d12+3

Proficiency with a Longbow allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Ammunition, Heavy, Range, Two-Handed, Slow