On the Special Ops level, "Armor Piercing", take the Barret .50 and kill the first Juggernaut. Then, continue to the scaffolding on the outside deck of the oil rig. Plant claymores along the path the Juggernauts take (which would be from the gate and along the inside wall, on the pillar opposite from the scaffold, and up the scaffold ladder). Plant about three of them and wait. When he arrives, wait for him to get to the top of the ladder and shoot him in the head with the Barret. If it does not kill him, plant another claymore the next time. If it does, you will see the Juggernaut's body fly off in the direction you shot him, but he will not fly off. Instead, he will get stuck in a random object.