
hypophora |

Snap Shot would probably give you more mileage as you must be pretty close to your enemies with a pistol, but unless you have feats that makes reloading and shooting not provoke I'd refrain from going down that route.
You could take Snap Shot and then go down Overwatch Style, picking up the Weapon Trick (Ranged weapons) when possible. That would allow you to boost your allies spell DCs by readying actions, potentially lowering the BBEG's saving throw by -16 for a save-or-suck spell.
That some sweet utility there!
Taking that into account I'm considering something like this:11/11 Gunslinger: Signature Deed
12/12 Gunslinger: Snap Shot
13/1 Fighter: Overwatch Style, Overwatch Tactician
14/2 Fighter: Overwatch Vortex
15/3 Fighter: Weapon Trick
16/4 Fighter: Weapon Specialization or Burrowing Shot or Advanced Weapon Training (Warrior Spirit)
17/5 Fighter: as 4 Fighter or Point Blank Master
18/6 Fighter: as 5 Fighter or Disruptive Shot