Gun Tank

Be Huge and Wield Huge Guns

Your body is a moving fortress, capable of wielding weapons far beyond normal limits. With sheer power and unshakable endurance, you function as a living siege engine on the battlefield. You are a living siege engine, a titan of muscle.

Level 3: Heavy Gunner

You can lug around massive guns and shrug off incoming bullets. This feature gives you several advantages:

Armor Training. You gain training/proficiency with Medium and Heavy armor.

Strong Attacks. You can use Strength, rather than Dexterity, for attack and damage rolls using Ranged weapons. You can also add your Strength, instead of Dexterity, to your Maneuver save DC. (Use custom "Gun Tank" versions of Firearms, as provided.) 

Level 3: Walking Turret

Your experience with mounted weapons grants you the following benefits.

Mounted Arsenal. While you are holding a Ranged weapon whose mastery property you can use, you can use the Mounted mastery property with that weapon. While a weapon is mounted in a fixed position, its damage dice increase by one step (d4 → d6 → d8 → d10 → d12, to a maximum of d12s). (Use custom "Gun Tank: Mounted Arsenal" versions of Firearms, as provided.) 

Move While Mounted. You can move a weapon with the Mounted mastery property that is in a fixed position. While moving with such a weapon, every foot of movement costs 1 extra foot. 

Level 6: Thick-Skulled

You possess exceptional mental and physical resilience. You roll with advantage on saving throws against being charmed, frightened, or stunned.

Level 10: Bulletproof

When you use your Bite the Bullet maneuver, you have Resistance to Bludgeoning, Piercing, and Slashing damage until the end of your next turn.

Level 14: Gatling Shot

Once on each of your turns, when you hit an enemy with a ranged attack using a weapon, you can make another attack with the weapon against the same target. This attack is always made with Disadvantage, regardless of circumstance. If this attack hits, you can make another attack against the same target, attacking again if you hit, and so on, until you miss or make a total of five attacks against the target.