Cabal Slug Shotgun
From Destinypedia, the Destiny wiki
The Cabal Slug Shotgun is a weapon commonly used by Legionary and Phalanx soldiers of the Red Legion. They can also be seen in the hands of some elite Psions, like the Psion Couriers in the Mars Adventure Psionic Potenial.
Minor users fire either single blasts or bursts of two shots. Taking a full blast does some serious damage and is a good way to die quickly. A more aggressive burst of four rapid shots is fired when a Centurion wielder is floating or when the target is on a Sparrow. Two of these bursts is enough to destroy a Sparrow, so be careful.