The only legitamate gun to quickscope with is the intervention, seeing as you can spam the barret and any other sniper if you miss the initial shot. If you can't kill someone in one shot, you shouldn't be sniping, and if you can kill someone in one shot, there's no reason for you not to use the intervention :) You can't spam when you are only scoped in for the same time as you would with the Intervention. People who are good with QS'ing on the Barrett only need one shot, anyway.