The breech face/slide or the bolt moves back in the case of semi-automatic guns, making the extractor of the firearm pull out the cartridge case. In other types of guns, this action is manually performed by the shooter.
Before the backward movement of the slide or bolt/breech face ends, the cartridge case which is being pulled by the extractor, comes in contact with the ejector of the firearm, pushing the spent cartridge case out via the ejection port.
During backward movement of the breech face/slide, the striker or hammer of the gun gets engaged by the sear, and cocked to help the resumption of the operation cycle. With other weapon types, it is the shooter that performs these actions manually. In the case of double action and double action/single action guns, the cocking and firing steps are incorporated into the trigger pull action.
Discussed above are the major steps in the operation of a gun. While choosing a firearm, you need to take into account the “action” of the gun as well, as opposed to just magazine capacity, barrel length, and sight construction. The number preceding the action of the gun describes the movements made by the striker or the hammer when the trigger is pulled. In the case of a single action gun, every trigger press makes the striker/hammer move right away in a single direction. Alternatively, in the case of double action guns, every trigger press would cock the striker/hammer and then release it, moving the striker in two directions.
Single action guns are also called “single action only”, or SAO. They usually require a lot less trigger pressure, which ranges from 2 to 4.5 pounds, making these guns ideal for competitions and well trained weapon users. 1911 style pistols are the most common single action pistols.
Double action guns are also called “double action only” (DAO). These guns usually need heavy trigger press, with the required pressure typically ranging from 5 to 9 pounds. There are also Double action/Single action (DA/SA) guns for shooters looking to have the best of both worlds. DA/SA guns each feature a decocker, which when engaged, locks the firing pin of the gun. The most common among the DA/SA are the CZ, Sig Sauer, H&K and Beretta lines.
There is a gun made for every style of shooting, and you should be able to find one that suits your needs and requirements. Regardless of the type or action of the firearm, training, education, and proficiency are necessary to use your gun effectively and safely.