What purpose does it serve? It's a LOT larger than most people realize, easily twice the size of a normal Derringer.
Since you can get shotshells in almost any caliber, it's not even a "snake gun". It's just a novelty IMO
Bond Arms makes very high quality derringers, and they have interchangeable barrels so you can have yours in several different calibers without buying more than one frame. Accuracy of the pistol-caliber Bonds is quite good.
However...they have a heavy trigger pull, plus they are big, heavy, and impractical. They are a novelty gun, pure and simple. I have killed many hundreds of poisonous snakes (I lived right on a swamp in Florida for a time...the rattlers and moccasins were thick) and the best handgun round I found was the 22 Mag shotshell by CCI. The rimfires use #12 shot and the mag holds a lot of them and drives them very fast. From ten feet the cloud of pellets simply engulfs a snake's head and neck resulting in instant incapacitation/death.
A convertible Ruger Single Six would be a great choice for snake control. The fact that you can use it for other shooting entertainment is a real bonus.
Addendum: If you handload you can make handgun shotshells superior to anything on the store shelves. Simply use copper gas checks (first one seated lip-up, second one seated lip-down over the shot) and number 12 shot and you have a devastating snake-killing cartridge. My 45 Colt snake loads hold over 400 pellets and are effective on big serpents out to at least fifteen feet.
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