Early patents of the Browning semi-auto pistols. Patent #580923 - gas-operated toggle system. Patent #580925 - Rotary barrel. Patent #580926 - Blow back pistol. Patent #580924 - Short recoil unlocking. Early production of the Colt semi-auto pistols. Comparing the early Colt 1900 of production vs Patent #580, 924. 38 ACP cartridges vs. 38 Super. The firing pin safety.