AMPs

We will start off with the AMPs since some of them are needed to flesh out the build.
Filling out Tier 1 in Assault since the main role for this build will be damage. Starting out you could probably just go with the 3 Assault Power spots to open up Tier 2. If you manage to unlock 2 of the 3 Tier 2 AMPs before you have invested too many points, you can head straight for Assassinate. I know I had to get Critical Surge from Whitevale though and that will leave you with spare AMP points that you can spend before you actually unlock it.
Critical Surge: Good as long as you make sure you are bringing up your crit rate with gear, it should give a boost to your spell surge.
Trigger Fingers... Good Luck. That's all I have for you. There are plenty of theories about how to get it, but 30 plat (depending on server) is the fastest way. It would be a great addition to a lot of builds but I don't see them raising the drop rate with how good and popular it is.
Deadly Chain: Part of the reason for the moves I picked in this build, landing physical attacks raises physical damage.
As for Tier 3 Assault, Assassinate is needed for the move, and the other two will be used throughout the full rotation.
Then because we will be using this build in PvE, we move over to the A/S AMPs
Crit Hit will help Critical Surge go off and Crit Severity is a given when you are working on actively getting consistent Crits to keep your buff up.

Keeping your buffs up will be a big part of your damage. You'll have a big opening burst and if done correctly you will be able to setup more as the fight goes on.

Abilities

I'm not going to reexplain what the ability tells you it does, but I will explain why this rotation.
Opening
x3 >> Spell Surge >>>>>>>>>> (if you have hate)>> Spell Surge Off (if needed) >>>>

is used right off the back to start you're more powerful attack off with 3 stack from Deadly Chain. Like I said above, the moves were picked to work directly with this, so everything will go off with this buff on and help keep it up. There is no real reason to Spell Surge this ability and having it active for is much more efficient.
this is the next step up in damage from . At this point you should start building up stacks from Surge Damage, Gunslinger, and Critical Surge will be going off.
is your last move to build all the buffs you can before using the last two moves.
This is about the point where you will be close to or already grabbed hate from a boss depending on the tank. and need to be used as quick as possible, using all charges of each. At this point it all depends on your tank really. If he managed to keep hate during all of that shooting, don't worry about . On the other hand, opening with this combo is an extreme amount of burst damage and chances are you will probably be pulling the boss. If this happens use to clear yourself from the threat table. Make sure Spell Surge is off at this point, then pop back into battle. Use to set Trigger Fingers off if you have it and get ready to do it again.
You will need to learn good times to try to get the full rotation off so as to not need to build stacks back up for and

Part 2 of being a DPS is to work with your team on when you will be