The Ruger SP-101 is a series of double action revolver

Revolver

A revolver is a repeating firearm that has a cylinder containing multiple chambers and at least one barrel for firing. The first revolver ever made was built by Elisha Collier in 1818. The percussion cap revolver was invented by Samuel Colt in 1836. This weapon became known as the Colt Paterson...

s produced by the American

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 company Sturm, Ruger

Sturm, Ruger

Sturm, Ruger & Company, Incorporated is a Southport, Connecticut-based firearm manufacturing company, better known by the shortened name Ruger. Sturm, Ruger produces bolt-action, semi-automatic, full-automatic, and single-shot rifles, shotguns, semi-automatic pistols, and single- and double-action...

. The SP101 is a small frame and all-steel construction carry revolver, with a 5-shot (.38 Special

.38 Special

The .38 Smith & Wesson Special is a rimmed, centerfire cartridge designed by Smith & Wesson. It is most commonly used in revolvers, although some semi-automatic pistols and carbines also use this round...

, .357 Magnum

.357 Magnum

The .357 S&W Magnum , or simply .357 Magnum, is a revolver cartridge created by Elmer Keith, Phillip B. Sharpe, Colonel D. B. Wesson of firearms manufacturer Smith & Wesson, and Winchester. It is based upon Smith & Wesson's earlier .38 Special cartridge. The .357 Magnum cartridge was introduced in...

, and 9x19mm Parabellum), 6-shot (.327 Federal Magnum

.327 Federal Magnum

The .327 Federal Magnum is a cartridge introduced by Sturm, Ruger and Federal Cartridge, intended to provide the power of a .357 Magnum in six shot, compact revolvers, whose cylinders only hold 5 rounds of the larger .357 Magnum cartridge...

 and .32 H&R Magnum

.32 H&R Magnum

The .32 H&R Magnum is a rimmed cartridge designed for use in revolvers. It was developed in 1984 as a joint venture between Harrington & Richardson and Federal Cartridge...

), or 8-shot (.22 LR) cylinder.
The Ruger SP-101 was introduced in 1989 as the smaller frame counterpart to the GP-100. Both of these revolvers, together, replaced Sturm, Ruger & Co's long-standing staple in the American firearms market, the Ruger Six series

Ruger Security Six

The Ruger Security Six and its variants, the Service Six and Speed Six are a product line of double action revolvers introduced in 1971 and manufactured by Sturm, Ruger & Company...

 revolvers.