barrel by an indexing mechanism linked to the weapon's trigger (double-action) or its hammer (single-action). These nominally cylindrical chambers, usually numbering between five and eight depending on the size of the revolver and the size of the cartridge being fired, are bored through the cylinder so that their axes are parallel to the cylinder's axis of rotation; thus, as the cylinder rotates, the chambers revolve about the cylinder's axis. Semi-automatic After the revolver, the semi-automatic pistol was the next step in the development of the pistol. By avoiding multiple chambers—which need to be individually reloaded—semi-automatic pistols delivered faster rates of fire and required only a few seconds to reload, by pushing a button or flipping a switch, and the magazine slides out to be replaced by a fully-loaded one. In blowback-type semi-automatics, the recoil force is used to push the slide back and eject the shell (if any) so that the magazine spring can push another round up; then as the slide returns, it chambers the round. An example of a modern blowback action semi-automatic pistol is the Walther PPK. Blowback pistols are some of the more simply designed handguns. Many semi-automatic pistols today operate using short-recoil. This design is often coupled with the Browning type tilting barrel. Machine pistol A machine pistol is a pistol that is capable of burst-fire or fully automatic fire. The first machine pistol was produced by the Austro-Hungarian Empire in 1916, as the Steyr Repetierpistole M1912/P16, and the term is derived from the German word maschinenpistolen. Though it is often used interchangeably with submachine gun, a machine pistol is generally used to describe a weapon that is more compact than a typical submachine gun. How it works: The shooter will disable the safety switch and pull the trigger, but hold it unlike firing a normal semi-automatic. The handgun will fire one round, and recoils, and the high-capacity magazine spring pushes another round, and is chambered, and fired without any actions needed from the shooter. They are useful in situations where multiple bullets must be fired in quick succession with minimal effort. Multi-barreled Multi-barreled pistols, such as the Pepperbox, were common during the same time as single shot pistols. As designers looked for ways to increase fire rates, multiple barrels were added to all guns including pistols. One example of a multi-barreled pistol is the COP .357 Derringer. Harmonica pistol Around 1850, pistols such as