Zombie Sniper

You are in a zombie apocalipse. You are a sniper and the only one that can protect the camp from zombies!

Kill the zombies with your rifle! But your ammo is limited. Some friends are comming back with food and ammo - don't  shoot them! Protect them!

Each friendly that reach the camp gives you 3 rounds of ammo. You can have a maximum of 10 rounds. Don't miss too much shots!

I know the sounds are not minimalistc (8-bit), but I don't care lose some points, because the sounds are amazing.

Update:

=> Changed Zombies behavior;

=> Changed spawn algorithm to avoid a streak of bad luck and lose because few friendlies was spawned.