Keystones for the Veteran aren't nearly as powerful as the other classes, so some builds opt not to get them as it is acutally better with certain weapons and builds to instead opt for normal talents with your points.
Use your regenerating "Krak Grenade" to kill heavy armour, and your gun to shoot everything else. The gun gives rendering so it can handle Flak even better than normal.
At first glance picking the talent "Only in Death does Duty End" seems like an obvious choice to pick. Being able to revive teammates with a simple button press seems obvious. However, I think this build is much better off not grabbing this choice. There are a few problems with this choice. The first and most obvious is that it greatly increases your cooldown and limits your range. This makes the shout pretty bad unless someone is already down. Additionally it promotes passive gameplay, where you aren't buffing your teammates until it is almost too late, as someone already went down. When you skip this talent I find it best to use it almost on cooldown (unless there are no enemies around). This lets you restore thousands of toughness throughout a match, and has decent up time where all or most of your teammates have increased damage against all enemies. "Focus Target!" is highly spammable, and you will constantly generate your team toughness, as well as giving them constant damage buffs.
Press ability. Shoot highlighted enemies. Repeat. That's the entire game play loop for this build. If you have crit chance on your lasgun when you build this talent, you basically have unlimited ammo the entire match. The giant ammo pool as well as free crit bullets makes it so you can stow your melee weapon and not worry about a thing most matches. Any Helbore lasgun works great here. The MkIII does the most damage and gives you the most "sniper" potential. When onslaught is fully charged the Mk II shoots nearly as fast as the Kantreal XII. If you don't like the charge weapons, or can't seem to get Onslaught then feel free to bring the Kantreal XII (or one of the other lasguns).
The Plasma Gun is basically the Plasma Cannon. Just don't forget to bascially always hold down the special key so you don't go boom. The Keystone works amazingly for this build and lets you normally only have to bother reloading during elevators or loading zones. It feels like it was made for the plasma gun.
This build is very ammo hungry, the DPS when using Infernaus might make this the highest DPS build for Veteran that I have. If you are with a team that will let you hog the ammo your recon lasugn can go brrrrr and all your enemies shall burn before your power.
The "Krak Grenade" is easily the flashiest blitz on this skill tree. It will kill a crusher in one shot on T5 difficulty. The "Shredder Frag Grenade" is also a really good grenade, but the Krak normally helps cover some of weaknesses of this class better.
Stacking Toughness is good on Veteran. I like to take two toughness curios and one health curio. Changing out the health curio for a stamina curios is good too.