The Frankenstein of WWII

Before America entered the Second World War, Tony Stein was a a Golden Gloves Boxer and a Navy Reservist. So he was kind of hardcore to begin with, and then a good ol' man-makin' war came around, and it was like tempering steel in Grizzly blood. At some point during Stein's conquest of the Pacific islands, he discovered a downed Douglas Dauntless Dive-Bomber (proving alliteration is always fun, even in the face of genocide!) with its tail gun still intact. Stein took the gun, added the stock from an M1 Garand, the bi pod and sights from a standard machine gun, and a box to hold the chains of .30 caliber bullets.

The monster in question

This was a gun designed to be mounted on a plane in order to kill other planes. And somewhere along the line Stein figured that was as good a thing as any to heave up on his shoulder and go Nazi hunting. The Stinger had a Rate of Fire of  near 1,500 rounds a minute, which is well within Mini-Gun territory. To put that into perspective, here's a video clip of a gun with a rate of fire of 1,200/minute. It'll be around the 2:50 mark.

When the US launched its assault on Iwo Jima in February 1945, Stein was there with his improvised gun of doom. The power of the bullets tore fortified emplacements apart and suppressed the enemy combatants enough to allow demolition charges to be hurled in to finish the job. The Axis was probably grateful to see that charge after a few minutes of having all the air around them replaced by bullets.