The Gatling gun is amazing but takes hours to load, ten seconds to empty!
We've got a couple of the guns that fire plastic BBs too. They are more powerful than you might think. One of the ones we've got also came from Spain and it's more acurate than the more expensive on I bought here. I used to shoot flies with it! Not in flight obviosly.
I bought one of these for my daughter, she's cowboy mad. It's never fired a shot though as she's too young yet, never even bought balls for it: