Why Is the SP101 Revolver So Popular? It occupies an interesting niche when it comes to the gun market. Here's What You Need to Remember: The SP101 occupies a curious place in Ruger’s lineup. It is not a service weapon, lacking the beefiness and extra round necessary for law enforcement work, but the service world is now dominated by semi-automatic handguns. In 1988 Sturm Ruger firearms introduced what would become one of their most popular revolvers of all time: the SP101 compact revolver. The SP101 was a lightweight, small frame revolver that built upon the company’s reputation for robust, reliable firearms. Since its introduction, the SP101 has branched into a wide range of calibers, both rimfire and centerfire, capable a broad spectrum of roles.