Thorn can take you down with 2 shots, shot in a timeframe of 0,36 seconds. The dot will take over and kill you. So the gun you're looking for has to either have a killtime faster than that 0,36 seconds or it has to prevent the death from the dot. Statistically, there are only 2 non-one hit primaries that can beat thorn. The last word. It has a ridiculous 0,26 seconds time to kill that could outgun thorn with 2 shots before the thorn could fire the second shot. The second gun is the Red death. 2 shots from thorn do not kill instantly, but rather inevitably with a dot. 3 third shot is a sealing shot. Red death could kill the thorn user just before that critical third shot and stop the dot before it drains the rest health.