Arsonal

Forcerfull Shot: This weapon's base damage is force damage.

Right tool for the job: This weapon can magically switch between a revolver, a shot-gun, and a hunting rifle. This switch can be done as a free action.

Rulett: When this weapon is in its revolver form the damage it deals an aditional random damage (fire, cold, acid, poison, lightning, or radiant). The damage is decided by a roll of a d6. if the same damage type is rolled twice in a row the damage from the shot is doubled.

Up close and personal: When this weapon is in its shot gun form and you shoot an individual within 5ft you roll an additional damage dice. The target must make a strength saving throw equal to half the damage or 8+your weapon to hit modifier whichever is higher. 

Another one: When you roll a critical hit with this gun it automatically shoots again with no action bonus action or attack cost. When you roll a natural 1 the weapon bounces back and deals damge to you equal to 1d8+your to hit modifer.

Stay Back: As a reaction you may shoot an enemy that moves within 5 feet you you

Planned Shot: When you hit with a shot you gain a +1 to your attack rolls this stacks for each sucessful hit you make (max of 3) missing a shot or not shooting this gun for 8 hours resets the bonus counter. In your alternate form when you make a planned roll you may roll the ability die and add it to the planned rolls outcome.

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: Fighter specializing in ranged weaponry, Range, Two-Handed, Ammunition (Firearms), Reload, Sap