Introduced in 1972, the Security-Six was the original model of the new series. The majority of these guns were manufactured with adjustable sights, though a few early models were sold with fixed sights. Security-Sixes could be ordered with either service or "target" (combat) -style square butt grips. Nearly all Security-Sixes were chambered for the .357 Magnum cartridge, which also permitted the use of the shorter .38 Special cartridge. Ruger also chambered the Security-Six in .38 Special for some police orders by fitting different cylinders that could only accommodate the .38 Special cartridge. Barrel lengths available on the Security-Six included 2.75, 4, and 6 inches.