Don't run and gun. After sniping one or two victims change position as they will come for you. Try to just stay near one captured zone and snipe single targets. If more than one enemy is coming just run somewhere else, preferably where you're teammates are. Some maps just suck for this bounty. And I know this sounds like an a-hole but if your team is bad don't try to help them loose a little less, leave! I did it with a void rocket launcher (Truth).