What i normally do when it comes to high round around 40 and running low in ammo is an issue. Have one person on the lighthouse barrier glitch with an upgraded VR-11. Other person run around in the open area in front of lighthouse and pile up the zombies. Then run up to the VR-11 person, have him shoot you then turn around and blast away those piled up zombies with the instant kill mode you get from VR-11.
I do this all day with the ak74u. Plus when you're down just crawl to the person on the glitch and he'll revive you. Repeat til max ammo drop. Voila! Hope this help for those who have trouble getting to high round.