User blog comment:Damac1214/The Truth About the Zombies Mode AK47/@comment-3062440-20111015145313

Maybe it was cut-off from the game in the final stage of development for some reason. That would be why you can still have it, though the console, but with no firesound(and no-low damage, if i remember right?). Could be an easter egg, but that's kinda unlikely. It's common to developers leave files in the game about something they cut off... the AK-47 in zombies was possibly trashed.