Semi-automatic firearm

A semi-automatic firearm is a repeating weapon that handles its own loading process. It is also known as a self-loading or autoloading firearm. While these weapons can fire many shots in a row, they differ from fully automatic weapons in one major way. In a fully automatic weapon, the firearm continues to discharge rounds as long as the trigger is held down. In a semi-automatic firearm, the shooter must manually actuate the trigger for every single shot. This means each trigger pull discharges only one round. To fire again, the user must release the trigger to allow it to "reset" before pulling it once more.

The mechanism relies on the excess energy released during a shot to prepare the next one. This energy typically comes in two forms: recoil or high-pressure gas expanding within the bore. When a shot is fired, this energy is used to unlock and move the bolt. The moving bolt performs several tasks in a specific sequence. First, it extracts and ejects the spent cartridge case from the chamber. Next, it re-cocks the firing mechanism and loads a fresh cartridge into the chamber. This entire cycle happens automatically without any manual input from the shooter.

Most semi-automatic firearms use a closed-bolt firing system. In this system, a cartridge is already chambered before the shooter pulls the trigger. When the trigger is pulled, only the hammer and firing pin move to strike the cartridge. This method is generally more accurate because the center of gravity changes very little during the shot. In contrast, an open-bolt mechanism is common in fully automatic weapons. In an open-bolt system, pulling the trigger releases a cocked bolt from a rearward position. This movement pushes a cartridge into the chamber and fires it instantly. While open-bolt systems allow air to circulate and cool the barrel, closed-bolt systems are preferred for the accuracy required in semi-automatic use.

History shows a long progression of these mechanical designs. The first successful design for a semi-automatic rifle was created by Ferdinand Ritter von Mannlicher in 1885. He produced the Model 85 and later the Models 91, 93, and 95. In 1902, American gunsmith John Moses Browning developed the Browning Auto-5. This was the first successful semi-automatic shotgun and used a long recoil operation. This specific design remained the dominant method for shotguns for approximately 50 years until production ended in 1998.

Different types of actions were developed to manage these processes. For example, the Winchester Model 1903 and 1905 used a blowback principle. These were the first semi-automatic rifles designed specifically for the civilian market. Other weapons used gas-operated actions, which use the gas from the fired shot to move the mechanism. The French Fusil Automatique Modele 1917 was the first semi-automatic gun to be widely issued to infantry. Although it did not receive a favorable reception, its improved version, the Model 1918, was better received during the Moroccan Rif War from 1920 to 1926.

Military adoption of these weapons changed the nature of combat. In 1937, the American M1 Garand became the first semi-automatic rifle to replace a nation's standard bolt-action infantry weapon. Developed by John Garand at the Springfield Armory, this gas-operated rifle gave American infantrymen an advantage during World War II. Other nations also introduced semi-automatic rifles during the war, such as the Soviet SVT-38 and the German Gewehr 43. However, these did not fully replace the standard bolt-action rifles in those armies. In 1945, Sergei Gavrilovich Simonov designed the SKS, which was the first widely issued weapon to use the 7.62x39mm cartridge.

Today, firearms are categorized by their firing capabilities. Some modern service rifles, like the M4 carbine, are selective-fire. This means they can switch between semi-automatic and automatic or burst-fire modes. Most civilian versions, such as the AR-15, are restricted to semi-automatic operation only.

Because the term "automatic" can be confusing, experts often use different labels. In the context of handguns, "automatic" usually distinguishes a semi-automatic pistol from a revolver. To avoid any misunderstanding regarding the loading mechanism, many people prefer the term "autoloader." Understanding these distinctions helps clarify whether a person is discussing how a gun loads or how it fires.