There's several. Imo a fantastic single target sniper build is a Troubadour/Streetfighter with an arquebus.  Here the key isn't high accuracy but incredible reloading times and dmg per shot. If you have trouble hitting stuff you can enable the arquebus modal. You will be slower but still fast - compared to other gunners. The trick is to summon Whisps that simply fire at your character. They do little shock dmg. But they also distract on hit which is what the Streetfighter needs t