There are thousands of examples of DA/SA semi-automatics, the Walther PPK being the first, followed up by the Walther P38 . Modern examples include weapons such as Beretta 92 , among hundreds of others. Almost all revolvers that are not specified as single-action models are capable of firing in both double- and single-action mode, for example, the Smith & Wesson Model 27 , S&W Model 60 , the Colt Police Positive , Colt Python , etc. Early double-action revolvers included the Beaumont–Adams and Tranter black-powder muzzleloaders . There are some revolvers that can only be fired in double-action mode (DAO), but that is almost always due to existing double-action/single-action models being modified so that the hammer cannot be cocked manually, rather than from weapons designed that way from the factory.
The gains made by athletes in uncontrolled observations have been much more impressive. Weight gains of thirty or forty pounds, coupled with thirty percent increases in strength, are not unusual. Such case studies lack credibility because of the absence of scientific controls. However, it would be foolish to completely disregard such observations because the "subjects" have been highly trained and motivated see the articles on pharmacology of sport and sports medicine in the countries of the former Soviet Union for more information on anabolic steroids.