http://www.youtube.com/watch?v=I16_8l0yS-g

Giant Octopus countermeasure system would be the logical defense.

Gatling pistol?
And uh.... a pistol that shoots grenades.

Gatling grenade pistol.

Grenade launching gatling rail-pistol with a sniper scope.

Not quite a pistol, but this is essentially a Gatling grenade launcher... 3000rpm?!

gatling shrek 3

it didnt work...

That ain't not no gun there, so the rule don't apply.

Gatling grenade launcher launcher

FUND IT.

Metal Storm remotely operated turret firing XM-25 rounds, except 40mm instead of 25.

Prepare to utterly destroy anything at all within a half mile that's not inside three+ inches of armor.

I had this ridiculous idea of six GAU-8's strapped in such a fashion so it would look like a gatling, with each GAU-8 being one barrel of the monstrosity. Then the whole thing would rotate and shoot so much metal it would tear mountains down.

Chainsaw Launching, Gattling pistol equipped with a scope

Gatling Crowbar.

Y'know, Jets 'n' Guns Gold has a gun almost exactly like that, except that the bullets don't explode. GAU-8 rounds are explosive, right? Also, strap six of your contraptions together to get a double-meta GAU-8 Avenger. Then strap another six of those together for a triple-meta, and enhance all barrels with railgun technology, and light it all on fire for good measure. Burning Triple-Meta GAU-8 Avenger Gatling Railgun. That'll drill a hole through the moon in short order. :U

Strap a double-meta one facing backwards as well as rocket engines, then use it as a launchable missile, with FOABs strapped on the back to act as the payload.

Nope. They'll fragment, just like any other large-caliber round, and depleted uranium ones are incendiary, but there's no explosive load.