Semi-automatic firearm
Typically, this involves the weapon's action utilizing the excess energy released during the preceding shot (in the form of recoil or high-pressure gas expanding within the bore) to unlock and move the bolt, extracting and ejecting the spent cartridge case from the chamber, re-cocking the firing mechanism, and loading a new cartridge into the firing chamber, all without input from the user.
Semi-automatic rifles did not see widespread military adoption until just prior to World War II, the M1 Garand being a notable example.
Modern service rifles such as the M4 carbine are often selective-fire, capable of semi-automatic and automatic or burst-fire operation.
The Auto-5 relied on long recoil operation; this design remained the dominant form in semi-automatic shotguns for approximately 50 years.
In 1903 and 1905, the Winchester Repeating Arms Company introduced the first semi-automatic rimfire and centerfire rifles designed especially for the civilian market.
By the early 20th century, several manufacturers had introduced semi-automatic .22 sporting rifles, including Winchester, Remington, Fabrique Nationale and Savage Arms, all using the direct blow-back system of operation.
The first semi-automatic rifle adopted and widely issued by a major military power (France) was the Fusil Automatique Modele 1917.
This is a locked-breech, gas-operated action that is very similar in its mechanical principles to the future M1 Garand in the United States.
Other nations experimented with self-loading rifles between the two World Wars, including the United Kingdom, which had intended to replace the bolt-action Lee–Enfield with a self-loader, possibly chambered for sub-caliber ammunition, but discarded that plan as the imminence of the Second World War and the emphasis shifted from replacing every rifle with a new design to speeding-up re-armament with existing weapons.
During World War II, the M1 Garand gave American infantrymen an advantage over their opponents, most of whom were issued slower firing bolt-action rifles.
Designed by Sergei Gavrilovich Simonov in 1945, it came equipped with a bayonet and could be loaded with ten rounds, using a stripper clip.
However, the SKS was quickly replaced by the AK-47, produced at around the same time, but with a 30-round magazine, and select fire capability.
The bolt then recoils far enough rearward to extract and load a new cartridge from the magazine into the firearm's chamber, ready to fire again once the trigger is pulled.
With this system, pulling the trigger releases the bolt from a cocked, rearward position, pushing a cartridge from the magazine into the chamber, firing the gun.
