Firing
In a sense, extracting the empty case from the chamber after
firing is the inverse of feeding. In feeding,
a cartridge pushed towards the chamber and guided by
ramps, feed lips, and the cartridge itself, will
usually arrive at the chamber without additional
positive control of the round. However when the case
is extracted the only components guiding
its rearward movement may be the extractor and the
constraining presence of the chamber.
Also since firing case expands it against the chamber
walls under great pressure, freeing it requires
considerable force.
For these reasons removing the spent case requires an
extractor hook.
The extractor is attached to the bolt so that it slips over the rim of the cartridge when the round is fed or chambered. When the bolt opens, the extractor pulls and guides the case from the chamber.
There are various ways to design the extractor but in general it is a latch using spring tension to allow it to snap over the rim when moving forward but retain the rim when moving rearward.
Next Section:
Ejecting