These are wizards who fuse magic with fire arms, giving their spells a little bit more of a kick, do these weapons are often unstable and can misfire more often then other firearms.

Firearm proficiency

Beginning when you select this subclass at 2nd level, you gain proficiency with firearms allowing you to add your proficiency bonus to firearms.

Arcane Gunsmith

Starting at 2nd level, your years of studying and tinkering allows you to create fire arms and magic bull. 

Gunsmith

You gain proficiency with tinkerers tools. You may use them to craft ammunition at half the cost, repair damaged firearms, or draft or create new firearms (dms discretion).

Magic Bullets 

You can infuse spells into bullets creating magic bullets, you choose a projectile spell that deals damage that is instantaneous and you spend one spell slot to make 10 bullets of that type of spell, this allows you to use those bullets to cast those spells but doing so multiplies your misfire rate by 2 and this can lead to one of these effects if you roll lower then the misfire rate, the effect is determined by rolling a d20.

1. The gun blows up dealing 3d6 force damage to you and any creature 10 feet around you, the gun cannot be repaired 
2. The gun gets clogged because the bullet became a plant
3. The gun shoots out a pink dust that makes you (unless your a warforged or another race like it) and any creature that isn’t a beast, monstrosity, construct, or ooze that is 5 feet around you to start to think their a animal for 7 minutes 
4. The gun turns into a fish that shoots out the spell of the magic bullet  you where originally trying to cast, this last 6 minutes 
5. The gun becomes a water gun for 1 minute 
6. The gun gains a mind of its own and will try to shoot every one
7. You start to think you are a vampire 
8. The nearest paladin starts to think they broke their oath 
9. You are now wanted in the nearest village 
10. A snail somewhere is coming to kill you, till that snail does you can’t die of old age, if you would die any other way that wasn’t by the hands of the snail you will be brought back at sundown
11. The nearest river is filled with sharks
12. Everyone swears loyalty to the nearest nyth 
13. You have disadvantage on everything that requires you to roll dies for a day
14. You loose all of your muscles for a day
15. You forget all languages and can only speak bird
16. You become a potted plant for a minute 
17. You create a 300 foot anti magic field
18. You get a lollipop 
19. A wraith is summoned to attack you, if a creature that isn’t you try’s attacking the wraith a wraith will be summoned for them, the same rule applies to their wraith but with them
20. The spell attack deals the max amount of damage it can do

Potent Shot

Starting at 6th level, you can use your magic to charge up you firearm making it more powerful and more unstable. You can use a bonus action and a spell slot to make the gun your holding will deal double the amount of damage it would had dealt on its next attack but you increase your misfire rate by double.

Empowered Firearm

Beginning at 10th level, you craftsmanship with firearms allows you to forge more powerful weapons, you can create are more powerful, your firearms deal a extra 5 damage 

Fatal Spell Slinger

Starting at 14th level, you have achieved great skill in using your firearms and spellcasting. When you do a critical hit, deal max damage on a creature with a firearm or spell, or deal  damage to a creature with less hit points then the damage you dealt, you can do another action to cast a spell or do another attack with a firearm.