Magnum Opus "Hellbringer".666 Magnum Revolver

Magnum Opus "Hellbringer" .666 Magnum Revolver is massive double-action revolver, this huge weapon holds only three rounds in its solid titanium-steel cylinder, but each one is a .666 Magnum man-killer. It's a break-action design, engaged by a left-side thumb button. Each of the three steel-cased shells holds one .666-caliber lead slug which hits harder than most Magnum or Nitro Express hunting rifles! These rounds will put even the toughest armor to shame. The entire handgun is composed of steel and ultra-strong hybrid alloys (except for the ergonomic combat-style grips, which are made of neoprene), and the ported barrel has a heavy, full-length underlug for balance. While the Hellbringer comes with no fancy electronics, most owners supplement the blade-type sights with at least a laser sight; with only three shots, you have to make each one count!

Source

 * Solo of Fortune 2, pg.70
 * Blackhand's Street Weapons, pg.38