You've heard that firearms are volatile and unpredictable, but... this just seems excessive.

This weapon does not require ammunition. When fired, a single bolt of energy shoots out, dealing 1d6 lightning damage on a hit. Well, sometimes.

Whenever you hit a creature or object with the bolt fired from this weapon (including as a result of one of the below effects), roll a d20 and apply an effect based on the roll:

1. The projectile turns around before hitting, and instead treats you as the target of the attack. This attack counts as a critical hit against you.
2. The projectile becomes incorporeal, and continues in a line after hitting the target. If there is a creature in that line, make a new ranged attack roll against that creature.
3. The projectile misses the target by teleporting slightly left. If there is a creature within 5 feet and to the left of that creature, they become the new target.
4. The projectile misses the target by teleporting slightly right. If there is a creature within 5 feet and to the right of that creature, they become the new target.
5. The projectile acts as normal.
6. The projectile bounces after dealing damage, traveling directly back toward you. Make a new ranged attack roll against yourself.
7. The projectile becomes a foam noodle upon contact, dealing no damage.
8. The creature is pushed away from you by 10 feet.
9. The projectile teleports backward along its path after hitting, causing it to hit the target a second time.
10. The projectile acts as normal.
11. The projectile slows down rapidly, never actually hitting the target. 
12. The projectile bounces 90 degrees to the left. If there is a creature to the left of the target within 150 feet, make a new ranged attack roll against that creature.
13. The projectile bounces 90 degrees to the right. If there is a creature to the right of the target within 150 feet, make a new ranged attack roll against that creature.
14. The projectile stalls in place for the next round, restraining the target and causing them to take an additional 1d6 lightning damage at the start of their next turn.
15. The projectile acts as normal.
16. The projectile teleports after dealing damage, to a randomly selected creature within 30 feet of the target. This attack automatically hits the new target.
17. The projectile teleports after dealing damage, to a randomly selected creature within 60 feet of the target. This attack automatically hits the new target.
18. he projectile teleports after dealing damage to a creature of your choice within 30 feet of the target. Make a new ranged attack roll against that creature.
19. The projectile acts as normal.
20. The projectile deals 10 times its normal damage. If the attack roll was a critical hit, it deals 10 times the critical hit's damage.

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: Weapon Property: Light, Ignore Weapon Property: Two-Handed, Range, Two-Handed, Ammunition (Firearms), Reload, Sap