Here's a rare example of the Auto Mag, this is one that is custom built from the ground up for the .440 Cor-Bon cartridge, see it here:
>>94281This is probably the only AMC Auto Mag pistol chambered for this cartridge, and I imagine that it's a monster to shoot. It has no iron sights, only a red dot, presumably a rather robust one.
.50 Action Express is a powerful cartridge designed for the Desert Eagle pistol, it has a rebated rim (meaning it's smaller than the rest of the case), so that it can fit on the bolt-face of a .44 Magnum Desert Eagle, requiring only a new magazine and barrel.
A rather potent cartridge.
.440 Cor-Bon is based on the .50 Action Express, necking that cartridge down to .44 caliber, the concept being to drive that .44 caliber projectile to speeds that .44 Magnum could only hope to dream of, some loadings can be comparable to the mighty .454 Casull revolver cartridge, very impressive for an automatic pistol.
.50AE has remained in some popularity, in part for being a .50 caliber Magnum cartridge in an automatic pistol, which is about as big as is commonly available.
.440 never really took off though, Cor-Bon had problems with producing casings properly, and demand was just never high, Magnum Research and Israeli Military Industries (who were their manufacturer back in those days) would see some demand when they had no guns or conversion kits in stock, and then almost none when they actually did. Eventually it was discontinued altogether.
It's difficult to find these days.