The most difficult way to do this is to unload on them with your frags, stuns, and ammunition, but even then they do not always die. There is an easier way if you have a Thumper. Try to hit them in the head with it. This strategy is still difficult, but you can conserve ammunition. If you cannot seem to hit them with the Thumper, an even easier way is with a sniper rifle. About three to four shots in the head will take care of him. Almost every Special Op with a Juggernaut also has a sniper rifle.