You have a +1 bonus to attack and damage rolls made with this magic weapon.

The Tinkers Wheel lock is loaded with powder, wadding and magical shots through the muzzle of the weapon.
Once fired, the weapon must be reloaded before being fired again. You must have one free hand to reload the firearm. Reloading the weapon requires 1 bonus action. 

Magic Aim. As an Artificer, you can use your Magical Tinkering feature to imbue a shot with magical properties adding an additional 1d4 to attack rolls made with this weapon.

Misfire. Whenever you make an attack roll with this weapon, and roll a 1 or 2, the weapon misfires. The attack misses, and the weapon cannot be used again until you spend an action or bonus action to try and repair it. To repair your firearm, you must make a successful DC 17 Tinker’s Tools check. If your check fails, the weapon is broken and must be mended out of combat at a quarter of the cost of the firearm.

Ammunition. All firearms require ammunition to make an attack, and due to their rare nature, ammunition may be near impossible to find or purchase. However, if materials are gathered, you can craft ammunition yourself using your Tinker’s Tools at half the cost.

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: Bonus: Magic, Artificer with proficiency in Tinkers tools., Damage, Combat, Artificer, Range, Ammunition (Firearms), Reload, Sap