I've seen so many people who think you sit back with a sniper rifle and pick everyone off before going into the room. Then they are shocked when they run out of of time. I guess it's 'guides' like this that started that rumor.
Well here's the scoop. To get this optional you have to be quick. Going in with shotguns is about the most effective, unless you are in a premade team and eveyone knows their roles.
On Elite, everytime I've gotten the optional, it was using the snipe/trigger line method. Using the shotgun method I've never been with a team that got the optional.