Which of the following is the last cycle of operation?

The last cycle of operation in a sequence involving firearms, particularly in the context of a semi-automatic or automatic weapon, is the cooling phase. After a firearm is discharged, it generates significant heat due to the firing process. The cooling phase is vital, as it allows the weapon's components to return to a safe temperature and ensures reliable operation during subsequent firings. This phase involves the dissipating of heat from the barrel and other components, preventing overheating and potential malfunctions.

The firing, unlocking, and chambering processes occur prior to cooling. Firing is the act of discharging the ammunition. Unlocking refers to the mechanism that allows the bolt to move rearward after firing, and chambering is the process of loading the next round into the chamber. Understanding the sequence of these operations is crucial for the safe and effective handling of firearms.