Troubleshooter

A troubleshooter is an often overlooked type of rogue that specialises in the knowledge of security measures such as locks and traps. while many use this knowledge for criminal gain, exploiting their knowledge to crack safes or defeat traps of incredible complication, many who take this subclass actually work within the confines of the law to help set up such security, or perhaps even directly under the guards or nobles that uphold it. 

As lock and trap technology has advanced, troubleshooters all now require at least a relatively advanced knowledge of engineering and tinkering, and this has lead many to delve into the knowledge of experimental weaponry. as such, the firearm is quickly becoming a trademark weapon of the troubleshooter regardless of which side of the law they ply their trade. Now more than ever, the name "troubleshooter" has never been quite so apt... 

Security specialist

Starting at 3rd level, you become an expert at dealing with all manner of security and traps and also develop a decent understanding of engineering. you gain the following benefits:

• you gain proficiency with Tinkers' Tools
• you gain expertise with thieves' tools. if you already have expertise in thieves' tools, you may select another rogue skill or tool that you are proficient with to gain expertise in.
• you can attempt to pick a lock or disarm a trap as a bonus action.
• you have advantage on any checks required to prepare a trap for use, and cannot trigger any trap that you or a member of your party has set up. 
• you have advantage on intelligence (investigation) checks made to analyse any kind of security measures. For example, this could be to determine how a trap works in order to disarm it, find and understand the mechanisms for a particularly unique lock, or to analyse guard rotations in order to find exploitable flaws in patrol patterns. At the discretion of the Dungeon Master, you may also gain additional information compared to other members of your party if you succeed on such checks.

Firearm Proficiency

Also at 3rd level, your knowledge of engineering gained from studying how more complicated traps work has led you to uncover and study the use of equally complicated weaponry. you are proficient in the use of firearms.

Optional:

you become proficient in Exandrian firearms.

Shootist

Starting at 9th level, your proficiency with firearms has evolved into mastery. you gain the following benefits:

• Reloading a one handed ranged weapon with the loading quality no longer requires a free hand, so long as you are not incapacitated or restrained and have the ammunition available.
• using the bonus action granted by your cunning action on your turn, whenever you make an attack with a one handed ranged or finesse weapon and have a one handed firearm in your other hand, you can make a ranged attack with the offhand firearm. this attack cannot benefit from sneak attack.

Optional

• if you are wielding an exandrian one handed firearm in each hand, you may reload both firearms with the same reload action. this does not apply to the Blunderbuss or Hand Mortar.

Runebreaker

By 13th level, your encyclopedic knowledge of security now extends into finding exploitable flaws in even security systems created through magic. you gain the following benefits:

• whenever you find an object that has been trapped via the use of magic, you are considered proficient in the arcana checks necessary to determine what kind of spell or magic created the trap and what weaknesses it has
• you can make a tinker tools check to dispel any magical trap created by a spell. the DC for the check = 15 + the level of the spell that created the trap. successfully disarming this trap takes a minute. failing immediately triggers the trap.
• you have advantage on saving throws against magical effects caused by triggering a magical trap.

Flintlock and key

at 17th level, your mastery of finding and exploiting weaknesses (in both combat and in security) has lead you to one conclusion: if you put the shot in the right place, most locks are weak to bullets. you can automatically open any mundane lock, regardless of the DC for picking it, by shooting it with a firearm. while mundane traps are thwarted by this method, magical traps may still trigger when this method of destructive entry is used. if you use this feature in combat, this can be done as a bonus action. you automatically succeed if you are within 5ft of the lock, otherwise you must make a ranged attack with your firearm against the lock's armor class. (DM's Discretion)

You also learn to apply this exact same logic in combat to help your allies break down enemy defences; when you hit a creature with a ranged attack with a firearm and benefit from sneak attack, you can choose to only deal half your sneak attack damage. in exchange, the creature's armor class is reduced by 1 for one hour. this can be done multiple times, capping out at a maximum AC penalty of -3.