Arm Cannon

A magical arm-integrated laser cannon

Use an action to fire the cannon doing 3d8 radiant damage. Alternatively you can use your attack to charge the cannon. The Cannon takes an entire turn to reload. The cannon can hold 10 charges and deals and extra 1d8 radiant damage per charge. If fully charged the beam deals damage in a 5 ft wide beam for 120 ft. The cannon never runs out of ammo and any shot with more then five charges knocks the user back by (5 x number of charges over 5)feet and if the user comes in contact with a creature or object the user and whatever they hit take half the damage of the shot. This weapon requires two hands to aim without disadvantage. If you're proficiency with this weapon you can fire it one handed without disadvantage and you can charge with a bonus action instead of an action. If you're proficient with this weapon and you're wearing heavy armor you can use a bonus action to brace before firing, negating any knockback.

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: Loading, Range, Two-Handed, Ammunition (Firearms), Reload, Slow