A gum has a cartridge which consists of a primer, a projectile and a propellant. All the three are located in one metal package. I can tell you how a standard revolver works, even through; most modern arms have more or less the same way of operation. A revolver always has a cylindrical carrier for cartridges.
A series of several things happen inside the body of the revolver when the trigger is pulled. There is a hammer inside, which is pushed backwards by the trigger lever, squeezes a metal spring. The cylinder moves round, bringing the breech chamber in front of the barrel.
When the trigger is finally pulled, the hammer is released and the squeezed spring forces the hammer forward. The hammer slams into the back of the cartridge and ignites the primer; the primer sets the propeller off which leads to a gun shot.
A series of several things happen inside the body of the revolver when the trigger is pulled. There is a hammer inside, which is pushed backwards by the trigger lever, squeezes a metal spring. The cylinder moves round, bringing the breech chamber in front of the barrel.
When the trigger is finally pulled, the hammer is released and the squeezed spring forces the hammer forward. The hammer slams into the back of the cartridge and ignites the primer; the primer sets the propeller off which leads to a gun shot.