by Wiley Clapp - Wednesday, September 1, 2010
I remember reading in someone's old catalog that Colt used only seven different kinds of barrel stock for all those many calibers of the Single Action Army revolver.
I have never had the resources to completely verify this statement, but it seems reasonable. It also gets a guy thinking about the possibilities inherent in twin-cylinder “convertible” revolvers. The idea is easiest in Frontier-style revolvers where the cylinder comes out so easy. Ruger has made convertible 9 mm/.357 and .45 ACP/.45 Colt sets for years and I have a current production Colt SAA in .45 Colt with a second factory produced and fitted cylinder in .45 ACP. It allows me to shoot two kinds of ammunition in the same gun. The .357 Blackhawk was a popular gun when it came out, but was even more popular when Ruger made it with a 9 mm cylinder. As it happened, that was a time when the surplus stores sold World War II leftover 9 mm for as little as 2 cents a round (oh, for those days again!). In .45, you have always been able to find .45 ACP cheaper than .45 Colt ammunition. By the way, now that we have readily available .45 Schofield ammo, a Blackhawk Convertible is a three-caliber gun, because Schofield rounds will work perfectly in the .45 Colt cylinder.
To the best of my knowledge, no one has ever taken the extra cylinder concept to its full extension. Consider that a 9 mm/.357 Magnum Blackhawk revolver could easily be fitted with additional cylinders for common cartridges such as the .380 Auto and .38 Super, as well as a dozen or so unusual European rounds like the 9x21, 9x22, 9 mm Largo or others. They might even make the .357 Sig work.
Much is possible and actual production would have to be a function of demand. The principle that makes the concept work is a common bore diameter. If it runs to somewhere around .355 inches to .357 inches you can probably make almost any semi-auto pistol cartridge work. Of course a separate cylinder is required for each auto round, in order that the cartridges headspace in the cylinder on the case mouth.
I once reviewed an interesting custom cylinder that worked with most of these rounds. I do not believe that this product remains on the market. The least common convertible size is 10 mm, but I recall seeing a special run of Blackhawks in 10 mm with extra cylinders in .38/40. The bore diameter on that one is .400 of an inch and it was before the .40 S&W was introduced. Yep, now it could have an extra cylinder in that popular caliber as well.
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