Most warriors and combat specialists spend their years perfecting the classic arts of swordplay, archery, or pole arm tactics. Whether duelist or infantry, martial weapons were seemingly perfected long ago, and the true challenge is to master them. However, some minds couldn’t stop with the innovation of the crossbow. Experimentation with alchemical components and rare metals have unlocked the secrets of controlled explosive force. The few who survive these trials of ingenuity may become the first to create, and deftly wield, the first firearms. 

Gunslinger

You have a number of Grit Points equal to 1 + your Constitution Modifier x your Proficiency Bonus. 
You have various actions that you can perform, each costing a variable amount of Grit, but allowing you to do many things. 

Trigger Finger 
You now also have proficiency with firearms. 
When you roll a critical hit with a firearm, you can freely fire again and make another attack. 

Reload 
Reloading your firearms costs an Action and removes 1 Misfire charge if your gun was completely empty when reloading it. 
Pepperbox pistols have an ammo score of 6. 
Palm Pistols have an ammo score of 8. 
Laser Pistols have an ammo score of 4. 
Pistols have an ammo score of 5. 
Automatic Pistols have an ammo score of 12. 

Misfire 
When you miss an attack against a creature via a firearm, it gains 1 Misfire charge, with each weapon having a unique Misfire Score. When attacking with a firearm with at least 1 Misfire charge, you also roll 1d4 per charge, subtracting the result from your attack roll. When your gun reaches full Misfire and you miss an attack, it is broken and must be repaired with a set of Tinker's Tools. You can spend a Bonus Action as well as an Attack Action when attacking with a broken firearm to fire anyways, dealing half damage (rounded down) to yourself. 
Pepperbox pistols have a misfire score of 3. 
Palm Pistols have a misfire score of 2. 
Laser Pistols have a misfire score of 6. 
Pistols have a misfire score of 2. 
Automatic Pistols have a misfire score of 6. 

Repair 
Costing a set of Tinker's Tools, you can repair a firearm, removing a number of its Misfire charges equal to your Intelligence Modifier. If you are proficient with Tinker's Tools, you can remove an extra amount of Misfire charges equal to your Proficiency Bonus. 

Adept Gunslinger

You gain a few advantages when a fight breaks out. 

Combat Expert 
You can add your Proficiency Bonus to your Initiative Rolls. 
When a creature within 30 ft of you rolls a 7 or lower on their Initiative Roll, you can allow them to roll it again, but they must use the new result. 

Quickdraw
When combat starts, you can make a single quick firearm-related ranged attack against a single target, giving them the Surprised status effect. 
The critical hit threshold for firearm attacks is lowered to 18. 

Rapid Reloader 
You can now reload and repair firearms as a Bonus Action. 
When reloading a weapon, roll 1d20. On an 11 or higher, your next shot instantly counts as a critical hit and does not require a check roll. 

Gunpowder Expert 
Firearms have an increase of Misfire Score equal to your Proficiency Bonus. 
You no longer suffer a penalty to attack rolls when your equipped firearm has 1 or more Misfire charges. 

Uprising Hope

When those around you fail, it fills you with vigor. 

When a creature within 20 ft of you fails an attack roll, you regain 1 Grit Point and heal a number of 1d4s equal to your Proficiency Bonus in Hit Points. 

Forced Penance

Costs a Bonus Action. Until the start of your next turn, when a creature within 10 ft of you makes an attack roll on a creature other than you, they lose all bonuses in that roll but if it continues to succeed, they deal double damage. A creature targeted by this attack has +2 AC (after the they're hit) for the remainder of its duration. 

Spell Slinger

At level 18, you gain access to minor Spellcasting. Your Spells are shot out through bullet-shaped vials that explode on contact or in the air, depending on the Spell. As such, you can make a free firearm attack against a single creature while also casting a Spell targeting them.