Blowback is a system of operation for self-loading firearms that obtains energy from the motion of the cartridge case as it is pushed to the rear by expanding gas created by the ignition of the propellant charge.
The .380 ACP Colt Model 1903 Pocket Hammerless uses simple blowback. The mass of the slide is enough to delay opening of the chamber until pressure has dropped.
Cutaway model of the chamber with gas relief flutes (left) and roller-delayed action of the G3 battle rifle
Exploded view of primary components for bearing delay bolt carrier group
Operation of the Schwarzlose machine gun.
A semi-automatic firearm, also called a self-loading or autoloading firearm, is a repeating firearm whose action mechanism automatically loads a following round of cartridge into the chamber and prepares it for subsequent firing, but requires the shooter to manually actuate the trigger in order to discharge each shot. Typically, this involves the weapon's action utilizing the excess energy released during the preceding shot 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. To fire again, however, the user must actively release the trigger, allow it to "reset", before pulling the trigger again to fire off the next round. As a result, each trigger pull only discharges a single round from a semi-automatic weapon, as opposed to a fully automatic weapon, which will shoot continuously as long as the ammunition is replete and the trigger is kept depressed.
The Fusil Automatique Modele 1917 was the first semi-automatic gun that fires cartridges to be widely issued in the infantry of any nation's army.
SIG Pro semi-automatic pistol
Glock 18, a fully-automatic machine pistol from the mid-1980s (The picture shown is the Glock 18C)