A special one. There was a small outfitter back in the day who bought and converted five Automag V pistols to the .440 Cor-Bon cartridge, offering custom finishes and grips. They built only five of these pistols, and can imagine why, as you see through the ports of these slides, the pistols pictured here at the least do NOT have ported muzzles, meaning the recoil of this monster is worse still.
In terms of size and ballistics, this is about the closest you'll get to the .454 Casull automatic pistol as used by Alucard in Hellsing.
I'm equal parts impressed with these, as I am dumbfounded.