We've seen the world's smallest revolver already, and the Pfeifer Zeliska is the world's largest according to Guinness World Records. At over four feet in length, Zeliska copied the Remington model 1859...a bit bigger than it was produced the first time. If only Crocodile Dundee were still making movies to see it.
"Watch out, he's got a gun!"
"That ain't a gun. This is a gun."
"What are you talking about, that's just a knife! And they suck against guns!" [newlaunches]