Ok, so this is how i think this works.

As my action i target lock a ship.

I attack that ship, use target lock to reroll, but still miss.

I then am allowed to target lock that ship again, then use gunner to fire again and use the target lock to reroll any dice.

Does tbis sound right?

No... you can not gain the second target lock. In your example it would go -fire, -TL, -miss, gunner. The best way to do this would be fire, miss, gunner, reroll with TL.

Devon is wrong. Your first example is right.

Yeah, as far as I understand it, FCS kicks in after every attack. Since gunner is a separate attack, whatever it would kick in after you missed, as well as after gunner. Since you are not taking the target lock action more than once, you can use it as much as you want.

That said, I don't have my upgrades with me, so I might be missing some key wordage.

Yes. I admit I was incorrect. That's what I get for not reading the post title...

Yeah, as far as I understand it, FCS kicks in after every attack. Since gunner is a separate attack, whatever it would kick in after you missed, as well as after gunner. Since you are not taking the target lock action more than once, you can use it as much as you want.

That said, I don't have my upgrades with me, so I might be missing some key wordage.

If you have an android, some one made xwing squad builder. It has everything

According to the recent shuttle article on FFG's home page you're correct. It triggers after both attacks.