Adam Savage did a myth busters episode to see which was more efficient hacking the living dead with a machete or shooting them. They were using a nerf gun and a sponge axe. The thing that struck me odd with the sponge axe was. They never had to put their foot on the chest as the pull the knife out of the cleaved skull. They confirmed hacking Zombies would be faster. But I still say didn't account for the efficiency of bullets cutting through the bone.
Well, let's also talk stopping power. If the zombie touches you, they win. So, .45 cal will put them down when hit. With 9mm, 5.56mm, etc. they might still come at ya. There is a reason the mobsters of old shot 45 submachine guns. Goes through car doors and light cover easily. You just have to control the muzzle rise with short, controlled bursts. Spray and pray wastes a lot of ammo. Backup is a .45 Colt - 7 rounds but all deadly.
#humor