 It was designed by Harry Sefried, who previously worked for High Standard Manufacturing Company, where he designed the High Standard Sentinel revolver.The grip profile of the Sentinel was used on the "Six" line of Ruger .357 double-action revolvers, which included the Ruger Security-Six and its variants, the Service-Six and Speed-Six.These revolvers were produced from 1970 to 1988, and were unlike other double-action revolvers in that they used a one-piece frame, rather than a removable sideplate, which lent them superior strength.