I dunno if most part of people in this thread are complete noobs or just trolls. You already can outrun them sprinting - they probably can get you at some point, but they still won't be able to hit you. Furthermore - I have no problems with killing any amount of zombies as long as I have enough ammo: you can just move walking and shoot them, while one tries to hit you, you just move a bit away. Zombies are actually must be buffed, not nerfed, they are already too weak and as soon as you get game mechanics you don't have to play in team doing some raids - you are quiet good against them alone.
