Colt's first effort toward a metallic cartridge revolver was by conversion of existing percussion revolvers. The first of these conversions was patented on September 15, 1868 by Colt engineer, F. Alexander Thuer as patent number 82258. The Thuer conversion was made by milling off the rear of the receiver and replacing it with a breechplate containing six internal firing pins. The cartridges were loaded through the mouths of the chambers. Colt made 5000 of these but they were not well accepted. Colt found the mechanism so complex it included a spare percussion cylinder with each revolver.