Kill 4 enemies in a row while downed in Special Ops
You need a friend to do this achievement. You can only be down if you have a friend to revive you. There is plenty of missions this achievement could be completed in, you just need a lot of enemies and a good spot where you are in cover for their fire.
I did it in the Charlie mission Homeland Security, almost the same way as shown in the video tutorial below. But it is hard to shot the targets in long-range with just a pistol. A little trick: Empty your secondary weapon completely for bullets before you go down. That way MW2 is forcing you to use your primary weapon. Empty your pistol while you are running to your spot. When you are ready and the enemies nearby, get your partner to knife and down you. Now kill 4 enemies with you primary weapon.
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