A single Ranged Attack action doesn't need to be considered a single firing of a weapon. It's an abstraction that lets the game move along.

Take the zombie card Resilient for example: it takes a kill and turns it around to narrate that the Hero emptied all of xir available ammo to kill the zed, implying multiple rounds fired. Similar logic can be drawn out to account for the lethality of all weapons. It's all abstractions.

It's not a single shot.. If you've got Laying Down the Law as Anderson or Rachelle and a Revolver, you can shoot once (Twice if you're Anderson with Advanced Abilities, and let's not even get into Duct Tape...) a turn every turn and never go out of ammo...

There are some concessions made to mechanics instead of reality... The mechanics of the Shotgun are that you have to try not to group up as the zombies.

We played a variant game with 35 zombies (Mechanik on the forums bought several different colours) and I ended up getting about 20+ onto one square with the card that lets you pull all your zombies from 2 squares in.. Needless to say, it didn't end well for the people on that square, but the next turn resulted in quite the pounding for the zombie team...

You haven't seen shotgun efficiency until you lose more zombies than most scenarios let you play with in one volley