I just use the first sniper that you get, as I feel that is the best in the game. Plus I play in hardcore mode most of the time that's why I can get two kills with the one shot.
What I love doing best with campers is pulling the pin on my grenade, waiting 5 seconds, throw, and it blows up in their face without them having a chance to escape
What irritates me most on this game is those people with the noob tube(grenade launcher attachment).
I remember when someone fired one at me, I knew I was doomed but I managed to kill they guy before the round hit me. Bullet faster than grenade round