Arcane Machine Gun

The Arcane Machine Gun is a machine gun designed by Dwarven artificers to be the ultimate bane to all battlefields! Using a combination of Arcane energy and tinkering, the Dwarves were able to a create a machine gun that shoots Magic Missiles and able to be reloaded, albeit, it does take some time.

The Arcane Machine Gun has 10 charges and takes an action to fire. When fired, the player must choose how many charges they wish to expend. Each charge creates a magic missile that does 1d4+1 damage and automatically hits no matter the AC, unless the DM says so because of lore reasons, it's counterspelled, or the target has the shield spell on. 

The magic missiles that are fired can hit multiple targets within a 120 foot radius that can be seen, however, once a target has been chosen, it can not change targets under any circumstances.

Reloading: If under the maximum charges are fired and now the gun is empty, the gun overheats and does 10 fire damage that ignores resistances and immunities to the holder. If all 10 charges were shot off, all the darts become 1d6+1 damage, and can not be stopped by shield or counterspell, but the gun really overheats and does 2d8 firedamage to its user for two turns. During these two turns, the maximum amount of charges is halved and all attack rolls and skill checks are at disadvantage.

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: being trained no how to use it or by experimentation, Damage, Combat, Artificer, Range, Two-Handed, Ammunition (Firearms), Burst Fire, Reload, Slow