Path of the needle

 You were born in the bad side of the Damaran society, street orphan, always in issue with justice.
 To survive, you understand that fighting the Order is not something to do in a frontal way.

 Firing from distance, hiding in shadow was a better way, your way

 Using you criminal contacts to succeed to force gnome guilds to teach you how to twink your hand crossbow beyond common use.

Specialized Bolt

At level 3, you gain

Dual shooter

You learn how to fire at your target using two hand crossbow without losing time to reload.

 Rapid Shooter

If you don't use shields, you may ignore the loading properties of your hand crossbow

 Specialized Bolt 

Using time, materials and skills, you may build specialized bolts
In a gnomish way, using tinkering tools ( you gain proficiency in that tools), you may create the following bolts :

 - Grappling hook bolt : when fired, this bolt deploy three small arms basically creating a grappling hook. the bolt is fitted with a small metallic line that may be used to climb. due to the added weight, the range of this bolt is only 30% of the nominal range.
cost : 1 gp    may create up to 2 bolts in a short rest

 - Banshee bolt : some small holes are carved into the bolt, when fired this bolt emit a howling sound. It may be used to signal something and disturb animals.
 cost : 1 sp    may create up to 5 bolts in a short rest

 - Flare bolt : when reaching its maximal range (or after 10s if didn't reach max range) this bolt explore in a burst of light that persist 1min and slowly fall to the ground.
 cost : 1sp    may create up to 5 bolts in a short rest

 - Poison injection bolt : you may add inside the bolt a poising substance. it will be delivered on impact. even if the original poison is not directly applicable on weapon. (= you may use inhaled, ingested, contact, injectable poison). The bolt is sealed to protect the poison of oxydation, allowing the bolt to be prepared in advance.
cost : 5 sp (not including the poison cost)     may create up to 2 bolts in a short rest

At level 5, you gain Extra attack
When using your bonus action to shot extra bolt, you may shot a second one.

At level 7, you gain  Hawk's eyes
If you only fire one shot during your turn you may double the range of this shoot.

Sniper's nest

(based on sniper's nest feature from the Sniper archetype from Truemillux (found DnD beyond)

At the 9th level you have developed a keen eye for discovering tactically advantageous positions such as abandoned bell towers, the tops of tall trees or overhangs on a cliff face. You can spend 1 hour outside of combat constructing and camouflaging a Sniper’s Nest. Your DM will tell you if a space is appropriate for a Sniper’s Nest. While in your nest you gain the following benefits.  

• you need half as much food and sleep to sustain yourself
• you can see up to one mile away with no difficulty, able to discern even fine detail as though looking at something no more than 100 feet away from you. Additionally you have advantage on perception checks  for hostile creatures
• you are invisible

Theses benefits end when you leave your nest, attack or cast a spell.

Improved criticals

At level 13, you gain
When using a hand crossbow, your critical range increase to 19-20

Magical bolts

At level 17, you gain
Using time, materials, skills, you may create some magical bolts (properties found in DnD materials) :

 -    +1 magical bolt
 -    +2 magical bolt
 -    Dragon Slayer
 -    Giant Slayer 
 -    of Terror
 -    of Wounding
 -    Vicious
 -    of Lightning (as javelin)

Cost and time needed is DM fiat (based on they magical items creation rules)