What is the function of the bolt carrier group in a semi-automatic rifle?

The function of the bolt carrier group in a semi-automatic rifle is to cycle the action and chamber a new round. This component plays a crucial role in the semi-automatic cycling process.

When the trigger is pulled, the firing pin strikes the cartridge, igniting the primer and firing the round. The expanding gases from the fired cartridge push the bolt carrier group rearward. This movement is essential, as it not only ejects the spent casing from the chamber but also resets the system to prepare for the next shot. After the spent cartridge is ejected, the bolt carrier group moves forward again, chambers a new round from the magazine, and locks it in place, ready for the next trigger pull. This automatic cycling is what distinguishes semi-automatic firearms from manual breech-loading firearms, allowing for faster follow-up shots while still requiring one trigger pull per shot.

In contrast, the other options describe functions that are not directly associated with the bolt carrier group. Holding the magazine in place is the role of the magazine catch, while ejecting the spent cartridge is a result of the rearward movement of the bolt carrier group but is not its sole function. Compressing the recoil spring does not pertain to the functions of the bolt carrier group