Between 1972 and 1988, Ruger ran rampant on the revolver market with a new and innovative line of double-action wheel guns best known today as the "Sixes."
Introduced first with the square-butt Security Six and soon followed by the Police Service Six and rounded-butt Speed Six, these guns were born from what the Connecticut-based firearms maker described in their marketing ads of the day as the product of "Ruger engineers who started with a fresh sheet of paper and an unlimited budget!" in a move to ditch what was characterized as outmoded and obsolete designs and manufacturing methods.
More than just casting shade at industry standard-bearers like Colt and S&W who had been in the double-action revolver biz for almost a century, the hype was, to a degree, very real. The gun used a solid one-piece frame with the internal parts installed either through the top or bottom, which eliminated the need for a removable side plate, the latter of which was common to legacy designs.
Rather than a vent rib, the guns typically used a barrel with a forged integral rib and serrated ramp front sight. Security Sixes ran adjustable sights whereas Service and Speed Sixes had fixed sights.
At the height of the success of the Sixes during the Reagan-era, Ruger had more than 25 models in their catalog across three different calibers-- .38 SPL, .357 Magnum, and 9mm-- barrel lengths from 2.75- to 6-inches, and blued or stainless finishes. Some were outfitted with "speed hammers" from the factory, which didn't have a hammer spur. By 1985, over one million had been sold, an impressive figure achieved in less than a decade.
The guns were both affordable and gained a reputation for being reliable in service. As such, Ruger picked up several LE contracts including a special run of 3-inch Speed Sixes for the U.S. Postal Inspectors and a stainless .38SPL Security Six for the California Highway Patrol. There was even some limited use by the U.S. military for security details, leading to highly-collectible "U.S. Property" martial-marked examples floating around. Catering to export sales in India and the British Commonwealth, ".380" marked .38S&W Security Sixes were produced to replace aging Enfield and Webley break-tops in that caliber.
Nonetheless, all good things eventually come to an end and by 1988 the Sixes were snuffed out, replaced in Ruger's catalog by the similar but updated GP100 line, which endures today. Like the double-action Security/Speed/Service Six models they took the place of, the GP100s are well-respected, showing Ruger was on the right track when they broke the wheel gun mold back in 1972.