Cannon Master (Combat)Source Inner Sea Combat pg. 17 (Amazon)
You have learned how to keep firearm siege engines ready for battle despite harrowing circumstances.
Prerequisites: Siege EngineerUC, Knowledge (engineering) or Profession (siege engineer) 7 ranks, proficiency with at least one firearm siege engine.
Benefit: You gain a +2 competence bonus on any Craft (siege engine) checks made to repair a firearm siege engine. In addition, if you are the crew leader for a firearm siege engine with the broken condition, that siege engine’s misfire range is increased by only 2 instead of by 4, and the broken siege engine must misfire twice before it explodes.Source Weapon Master's Handbook pg. 24 (Amazon)
While acting as the leader of a firearm siege engine crew, you can spend 5 stamina points as an immediate action when the siege engine rolls a misfire to negate the misfire.