Zap guns are special, lightning casting weapons with which bodysnatchers (aliens) have armed themselves.
A zap gun is a 1 pound martial ranged weapon with a range out to 30/90 ft.
On a hit, it deals lightning damage equal to 2d6 plus the attacker's Dexterity modifier.
When an attacker rolls a 1 on an attack roll using a zap gun, the zap gun's energy cell becomes depleted and it must be replaced.

It’s up to you to decide whether a character has proficiency with a firearm. Characters in most D&D worlds wouldn’t have such proficiency. During their downtime, characters can use the training rules in the Player’s Handbook to acquire proficiency, assuming that they have enough ammunition to keep the weapons working while mastering their use.

Notes: Range, Ammunition (Firearms), Reload, Vex