This big case magnum auto pistol cartridge was in the works for at least two years before its 1979 introduction. It never become popular, mainly because there were precious few pistols in which to fire it, and is now obsolete.

At one time, Winchester offered two factory load for their .45 Magnum, a Supreme load using a 260 grain Nosler Partition Gold bullet and a Super-X load using a 260 grain JHP bullet. Both claimed a muzzle velocity (MV) of 1200 fps and muzzle energy (ME) of 831 ft. lbs., as measured from a five inch test barrel. At 100 yards the Supreme Gold bullet was still rolling along at 1033 fps and packing 617 ft. lbs. of energy.

With a 200 grain jacketed bullet the the Hodgdon Data Manual, 26th Edition shows that the reloader can expect a MV of 1244 fps from 16.0 grains of HS6 powder and 1409 fps from 17.5 grains of HS6. With a 260 grain jacketed bullet 24.5 grains of H110 powder should give a MV of 1290 fps and 25.0 grains of H110 should give about 1339 fps. The pressure of the latter load was measured at 37,400 cup. These velocities were measured in a five inch pressure test barrel.