Guns don't kill but they help Achievement
Guns don't kill but they help25
Kill 250 zombies using firearms.
If it fires bullets, it counts. Since there are so few bullets found in this game, your best option of doing this is reloading the checkpoint in City Hall with the mounted gun. Kill any immediate zombies, reload and repeat. You can get 15+ each time.
Note: Purna's rage skill counts toward this achievement.