pf2e.fyi
From Pathfinder Guns & Gears, which isn't enabled.

Advanced Firearm Familiarity

FEAT 12
Archetype Gunslinger
Prerequisites Gunslinger Dedication; expert in any kind of weapon or unarmed attack

You have familiarity with advanced firearms, treating them as martial weapons for the purposes of proficiency. You gain access to all uncommon firearms.

Pathfinder Guns & GearsORC