A pistol would be useful too. So would a sharp stick or a military knife. The best way to kill a zombie is to stab or shoot them straight in the head, hence the knife and pistol. sure auto shotguns, rifles, and maybe even sub-machine gun would be useful for pushing them back but but you need a pistol and stabbing knife for close range combat if the zombies get out of control or your weapons jam up or run out of ammo.