Sniper

There are many kinds of rogues, some stab backs, some pick locks. Snipers are masters of dominating a battlefield they aren't even a part of, making them legendary during times of war. 

Firearm Proficiency

When you choose this archetype at 3rd level, you gain proficiency with firearms.

Master of the Crows nest

Starting at 3rd level, you are nimble enough to acquire vantage points quickly and efficiently. You Are adept at hiding yourself by sitting perfectly still no matter what your hiding spot may be. Attacking an enemy while hidden does not reveal your position as long as you did not move during the turn in which you attacked. This ability does not mask the sound a firearm makes when used. 

Patience

You have mastered the art of patience. Starting at 9th level, If you spend your Action to track a targets movements and line up your shot, your Next Attack against the chosen target will deal critical damage, given that it hits.

Interception fire

You've grown potent enough that you cannot be ignored. Starting at 13th level, If you deal sneak attack damage to a creature, they have disadvantage on attack rolls until the start of your next turn.

Head shot

The head is the only logical target for a sharpshooter, and you've gained the ability to exploit that weak spot as efficiently as possible. Starting at 17th level, when you deal critical damage the amount of damage is tripled, or the amount of dice is tripled, whichever rule you use.