This is my sniper set up. Find cover, preferably higher ground. If it’s a good spot use Smart Cover and Support Station. This is your primary healing source. The back up is killing off a close by NPC with the sawed off shotgun. If they get close enough that you need this that’s a problem.
Land a headshot on a small fry that you can likely finish off with a single shot. This activates Disciplined and 30% damage for the next headshot. From here keep hitting guys you can one shot and work your way up. The damage output should be driving some NPC’s to seek cover rather than advance on you, except the heavies. By the time they’re close you should be at a full 100 stacks and take them down in 2-3 shots.
I will admit I’m not the greatest sniper in the game, but it’s a fun change from my other set ups.