Abstract: A robust and convenient caliber conversion kit is described, for example, for the higher-caliber GLOCK® semi-automatic pistol. The caliber conversion kit has an internalized spent round extractor for more reliability. In addition, the firing pin safety relies on a set of two-dimensional surfaces, rather than on a one-dimensional line or edge, for cooperation (interaction and support) with the firing pin and with a recess in the firing pin housing that receives the safety, resulting in more security. Also, the spent round ejector is snugly fastened around an outwardly-extending abutment of steel on the barrel, the abutment being within a recess also snugly fitting the perimeter of the front end of the ejector, resulting in a quieter ejector mechanism.