Arcane Hand Cannon

A creature proficient with the hand crossbow or heavy crossbow is proficient with this weapon. This cannon can be used as a heavy martial two-handed ranged weapon with the reload (5 shots) property (see DMG 267). It has a range of 80 feet, a long range of 320 feet, and it deals 2d10 force damage on a hit. Each shot consumes 1 of the weapon's 40 charges. After 5 shots, one of the loaded eberron dragonshards enters a cool-down period and you must spend an action or a bonus action realigning the cylinder's rings to use the next fresh shard. You can pull a special side lever to allow the cannon to regains 20 of its charges after an hour-long recharge cycle, during which the lever locks and it cannot be fired. The weapon only regains 10 charges during the next recharge cycle, then 5, after which point the weapon is useless until a skilled artificer removes and installs 4 new eberron dragonshards.

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: Replace Damage Type: Force, Weapon Property: Heavy, spellcaster that knows wizard spells, Damage, Combat, Range, Two-Handed, Ammunition (Firearms), Reload, Slow