Many maps don't often contain these weapons, and when they occasionaly do, players don't use them.
Really this only works vs juggernaughts and when you are playing with at least two other players.
Make sure your whole team has sentinel beams, then hunt down the juggernaught!
As long as you follow the target, the juggernaught will fall particularly quickly.
Doing this will make sure the juggernaught exchanges hands fairly quickly.