In the second half of the 19th century weapons in which a cartridge fed from a magazine was loaded into the breech by a working bolt replaced muzzle-loaded rifles. Such Bolt-Action rifles remained standard infantry issue until generally displaced by automatic weapons after World War II.
The loading mechanism is quite simple:
As the bolt is drawn back, a cartridge is fed into line with the bolt by a spring-loaded magazine.
As it is pushed forward, the bolt engages with the cartridge and moves it into the breech. .
In the final stage of the forward movement of the bolt, a protruding piece of the bolt assembly catches the trigger sear, so cocking the weapon. The bolt is rotated to lock the cartridge in the breech. The weapon can now be fired by pressure on the trigger. .
When the bolt is drawn backwards, a claw on the bolt engages the rim of the spent cartridge, so removing it from the breech. Once clear the cartridge is ejected.
This process is then repeated for the next cartridge until all cartridges have been spent, then a new magazine is clipped into place.