Quote by Meta:
Technically a shotgun shouldn't work since they don't even shoot bullets...
Only reason why I tried was because I read this on xbox360achivements.org - A lot of people confirmed it worked.
"Sally Likes Blood 15
Demonstrate killer economic sensibilities by taking down 3 enemies with a single bullet.
*This achievement can be achieved in Campaign, Zombies, and Dead Ops arcade*
There is a very easy way to get this in the Zombies Game Mode. While running around, find a spray weapon like a shotgun. Let the zombies follow around and around a certain area letting them bunch up more and more. Once there is a bunch of zombies, shoot at the upper torso/head of the zombies and you should take out 3 of the zombies with one of your shots."