Colt has released seven different revolvers named after snakes, and they have become a popular niche collection for many people. The Python is by far the best known, but several others are very rare. One of these is the Colt Viper, of which only a few thousand were made and only in 1977. The Viper is fundamentally a variation of the Police Positive Special with an aluminum alloy frame and a 4" barrel. They were all chambered for .38 Special, and in fact the only variations are in the finish - either blued or nickeled.