The Lightning Bow

This bow is a normal Longbow when not activated
Using a bonus action the user can activate the bow's lightning ammunition feature. The next time you make a ranged attack the weapon's ammunition changes into a bolt of lightning.  Make the attack roll as normal. On a hit the target takes 4d8 lightning damage.  On a miss the target still takes 2d8 lightning damage.  Other creatures within 10 ft. of the target must also make a DC 14 Dexterity saving throw or take 2d8 lightning damage. 
The weapon has 5 charges and used one charge per activation.  The weapon regains 1d4 charges every day at dawn. 
The user also has advantage on dexterity saves vs lightning when wielding the bow.