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I got to lever 30 last night with a friend doing this. If you're ending up in a loop of not having any ammo try this. Have one person get the ballistic knife that way you can kill the boss if your out of ammo. Go prone and keep knifing until you kill him. He wont take your knife away so it's great for the later rounds. It also works on regular zombies but it takes forever.
Also, remember to turn the power on obviously.
We're always looking for people to glitch with. My PSN is on my profile.