Colt started to number the slide, with receiver's serial number at about #C127300. This practice continued for commercial production through WWII. All 1911 commercial pistols after about serial C127300 to about C136000 (when 1911A1 production changes were phased in). First numbered slide pistols (in the C127xxx range) had the slide numbered on the bottom of slide rail. This only lasted a short time and numbering was moved to behind firing pin stop plate by serial C128000. Deduct 20 percent for a mismatched slide number. Changes between 1911 Commercial Government Model and 1911A1 Commercial Government were phased in during this period. A number of variations within these serial number ranges are of specific interest and are listed separately below. NOTE: Add 20- to 50 percent for finish 99-100 percent.