Adder Strike, Arc Slinger, Binding Throw, Body Shield, Bonebreaker, Break Guard, Chokehold, Cleaving Finish, Crusader's Fist, Death From Above, Death or Glory, Disengaging Feint chain, Dispelling Critical, Domain Strike, Drag Down, Felling Escape, Felling Smash, Feral Combat Training, Final Embrace, Final Embrace Horror, Final Embrace Master, Flanking Foil, Hex Strike, Horse Master, Impaling Critical chain, Improved Cleaving Finish, Jawbreaker, Monastic Legacy, Neckbreaker, Net Adept chain, Nightmare Fist chain, Performance Weapon Mastery, Performing Combatant, Pin Down, Pinning Knockout, Pinning Rend, Pinpoint Poisoner, Prone Slinger, Quick Bull Rush, Quick Dirty Trick, Quick Drag, Quick Reposition, Quick Steal, Rapid Grappler, Rebounding Leap, Rebuffing Reduction, Rending Fury chain, Revelation Strike, Sap Adept chain, School Strike, Siege Commander, Siege Engineer chain, Spinning Throw, Twin Thunders chain, Two-Weapon Feint chain, Vicious Stomp, Wave Strike, Whip Mastery chain: You either can't qualify or it isn't generally relevant to gunslinging.
Amateur Gunslinger: While you can't take it if you're already a Gunslinger, if you multiclass to pick it up, it can be a handy way to pick up either a free 1st level Deed (notice the Special text say 'can,' not 'must') and an extra point of Grit or trade it Extra Grit and 2 points of Grit. Win-Win!
Bludgeoner: Firearms deal bludgeoning and piercing, thus you can use this to knock people out without using Salt Shot, which is scatter only, anyways. Also works nicely with Sap Adept chain if you multiclass in the Sneak Attack.
Charging Hurler chain, Close-Quarters Thrower, Distance Thrower, Two-Handed Thrower: You're not that into throwing, you're more of a shooter kind of guy. Leave to Alchemists and Barbarians.
Clustered Shots: Kind of handy for bypassing DR, since it only applies once when using the feat. On the other hand, Dead Shot is also there for handling this kind of problem.
Combat Style Master: There are a couple of relevant Styles that you can actually make use of as a 'slinger, so this may be useful for switching between them and making sure the relevant one is up at combat start.
Deadly Finish: Melee-only and you get Grit from dropping foes to 0, you don't have to kill them for it to work.
Deathless Initiate chain: It's not bad, per se, but I've never been a fan of spending feats on situations that don't occur that often. Not to mention the attack and damage bonus is melee only. Best leave it Half-Orc Unbreakable Fighters.
Defensive Weapon Training: Dodge is always on and doesn't depend on my opponent's choice of maiming instrument. Pass.
Devastating Strike chain: If you decided to go for the Vital Strike chain, as opposed to Dead Shot, this may be worthwhile. It has a slightly more snipery feel to it, though it still doesn't work with Far-Reaching Sights, which is incredibly annoying.
False Opening: If you managed to make your way into Point-Blank Master (you didn't come from Close Quarters Thrower, right? Right?
), this can eat up AoOs that would be otherwise directed at your less nimble buddies but this seems like a lot of investment just for that. I think Dodge + Mobility is a better bet.
Fortified Armor Training: A
Gun Tank's best friend, this can work for other 'slingers as well but the Gun Tank can use it twice on their armor and shield.
Gory Finish: Unless you know you're going to drop an enemy, Dazzling Display would seem to be a better use.
Hammer the Gap: More damage that scales the more I hit? Easy prereqs? Yes, please!
Haunted Gnome: Not that good by itself, especially at low levels when you have very short durations.
- Haunted Gnome Assault: Now that's actually kind of useful as a free no-save debuff up to 3 times per day but even nicer with Deadly Stroke, though you can only get it off as a crit, unless you want to charge in for it.
- Haunted Gnome Shroud: Concealment up to 4 times per day, more if you pick up Arcane Talent or Magical Talent? Yes, please!
Impact Critical Shot: In combination with Critical Focus, this can add insult to injury if they survive the critical, though be careful you don't push your target out of Penetration range. If it's the last hit, tripping them for your melee buddies isn't a bad thing for finishing them off.
Landing Roll: I think I'd rather invest in not being tripped at all.
Moonlight Stalker: Not great requirements for you but you can activate it with Wind Stance, Lightning Stance (with Parting Shot) or Haunted Gnome Shroud for free attack and damage buffs.
- Moonlight Stalker Feint: Feint that still allows full attacks? Sure!
- Moonlight Stalker Master: Makes your concealment better and free movement, what's not to like?
Opening Volley: Only really useful if you're pursuing Sword and Pistol, though if you have to close you'll definitely still benefit regardless.
Passing Trick: Free feints are never a bad thing, though it's a lot of investment.
Prone Shooter: Your Admiral Ackbar senses should be going off like a tornado siren, for this is a TRAP. There aren't any ranged attack penalties for being prone.
Snap Shot: Requires a lot of investment but well worth it, as you threaten and can AoO with your firearm of choice.
- Improved Snap Shot: Even better than the original, you're what 3.5 Spiked Chain wielders were feared for but worse.
- Greater Snap Shot: Only works on AoOs but they hurt more than your normal attacks do. Not strictly necessary for Snap Shooters but it automatically improves with more BAB, so not a bad investment, either.
Sword and Pistol: Even more investment than getting the prerequisite Snap Shot. Deft Shootist is probably a better investment.